Fig. 398.—Pelvic Urethra and Posterior Part of Bladder of Horse Slit Ventrally and Laid Open.
e.d., Ejaculatory ducts.
The extrapelvic part (Pars cavernosa) passes between the two crura of the penis and runs along the groove on the ventral surface of the corpus cavernosum penis, inclosed by the corpus spongiosum and the bulbo-cavernosus muscle. It passes through the glans penis and projects forward about an inch in the fossa glandis as a free tube, the processus urethræ; this part is covered by a delicate integument, under which there is a thin layer of erectile tissue.
The lumen of the tube is largely obliterated in the inactive condition of the parts. When moderately distended its dimensions in a horse of medium size are as follows: At its origin the diameter is about half an inch (1 to 1.5 cm.). The pelvic dilatation at its widest part measures one and a half to two inches (ca. 3.5 to 5 cm.) transversely, and about an inch (2 to 3 cm.) vertically; it is elliptical in cross-section when fully distended. The isthmus at the ischial arch is a little smaller than the initial part. Beyond this the lumen is about one-half to three-fourths of an inch (ca. 1.5 cm.) in diameter, and is fairly uniform to the glans penis. Here there is a slight fusiform dilatation (Fossa navicularis), beyond which the tube contracts.
The opening from the bladder into the urethra is termed the internal urethral orifice (Orificium urethræ internum); it is closed except during urination. The terminal opening is the external urethral orifice (Orificium urethræ externum) or meatus urinarius. The two orifices of the ejaculatory ducts are situated dorsally on either side of the colliculus seminalis, about two inches (ca. 5 cm.) behind the internal urethral orifice; they are slit-like and close together. The small orifice of the uterus masculinus is placed centrally on the colliculus; it is inconstant. The orifices of the prostatic ducts are on two groups of small papillæ, placed lateral to the openings of the ejaculatory ducts. The ducts of the bulbo-urethral (Cowper’s) glands open on two lateral series of small papillæ, about an inch (ca. 2.5 cm.) further back and close to the median line. The small orifices of the urethral glands are situated laterally in the wide pelvic portion.
Structure.—The mucous membrane contains an unusually large amount of fine elastic fibers, and in its pelvic part there are alveolar glands (Glandulæ urethrales). The epithelium is at first like that of the bladder, then becomes cylindrical, and in the terminal part is stratified squamous. In the dorsal wall the membrane forms a median ridge, the urethral crest (Crista urethralis); this terminates about two inches from the internal urethral orifice in a rounded elevation, the colliculus seminalis, on the sides of which the ejaculatory ducts open.
At the origin of the urethra there is a layer of circular unstriped muscle-fibers outside of the mucous coat. Beyond this the latter is inclosed by a layer of erectile tissue, composed of plexuses of veins supported by trabeculæ of elastic and smooth muscular tissue. This is continued by the corpus spongiosum. Outside of the erectile tissue there is a continuation of the intrinsic unstriped muscular coat, consisting of external and internal longitudinal strata, with a layer of circular fibers between them.
Except at its origin and termination the urethra is provided with a continuous layer of striped muscle, placed outside of the erectile tissue. This is described as consisting of two parts or muscles.
(1) The urethral (or Wilson’s) muscle (M. urethralis) consists of dorsal and ventral layers of transverse fibers on the wide pelvic part of the urethra, and covers the bulbo-urethral (Cowper’s) glands. It is a compressor of the pelvic part of the urethra and the bulbo-urethral glands. By its forcible contraction it plays an important rôle in the ejaculation of the seminal fluid, and also in evacuating the last of the urine in micturition.[147]
(2) The bulbo-cavernosus muscle (or accelerator urinæ) is the continuation of the urethral muscle on the extrapelvic part of the urethra; it extends from the ischial arch to the glans penis. At the root of the penis it is the thickest, and forms a complete layer of circular fibers which inclose the corpus spongiosum and the urethra. Beyond this it diminishes very gradually in thickness, and consists of fibers which arise on a median ventral raphé and curve around the corpus spongiosum to end on the tunica albuginea of the corpus cavernosum. Its action is to empty the extrapelvic part of the urethra.
The ischio-urethral muscles (Fig. 452) are small bands which arise on the ischial arch and crura of the penis and pass forward to become lost on the ventral layer of the urethral muscle. They may assist in erection of the penis by exerting pressure on the dorsal veins.
MALE GENITAL ORGANS OF THE OX
The scrotum is situated somewhat further forward than in the horse. It is long, pendulous, and has a well-marked neck. The skin here is usually flesh-colored, but in some breeds is more or less pigmented; it is sparsely covered with short hairs. Just in front of it are four (sometimes only two) rudimentary teats.
The testicles are relatively larger than those of the horse, and have an elongated, oval outline. The long axis is vertical. The inner surface is somewhat flattened.
A testicle of an adult bull measures on the average about four or five inches (10 to 12 cm.) in length, exclusive of the epididymis; with the latter the length is about six inches (15 cm.). The width is about two and a half to three inches (ca. 6 to 8 cm.), and the antero-posterior diameter about the same. The weight is about nine or ten ounces (ca. 250 to 300 grams).
Fig. 399.—General View of Genital Organs of Bull.
The tunica albuginea is thin. The parenchyma is yellowish in color. The mediastinum testis descends from the anterior part of the upper extremity deeply into the gland as an axial strand about 5 mm. in thickness. The vasa efferentia leave at the upper end of the mediastinum.
The epididymis is very closely attached to the testicle. The head is long; it curves over the upper extremity and nearly half-way down the anterior border of the testicle. The body is very narrow, and lies along the outer part of the posterior border of the testicle, to which it is attached by a narrow peritoneal fold. The tail is large and is closely attached to the lower extremity of the testicle.
The spermatic cord and the tunica vaginalis are much longer than in the horse; the extra-inguinal part of the cord is about eight to ten inches (20 to 25 cm.) in length. The cremaster externus is well developed, and almost completely incloses the tunic to the nook of the scrotum; it does not extend so far down as in the horse, but is inserted about at the level of the upper pole of the testicle. The vaginal ring is relatively very small, and is about four inches (ca. 10 cm.) from the linea alba. The cremaster internus is feeble.
Fig. 400.—Internal Genital Organs of Bull; Dorsal View.
The right vesicula is sectioned frontally. The dotted line indicates the backward extension of the peritoneum.
The spermatic cords emerge through the outer angles of the external inguinal rings, and curve downward and inward to the neck of the scrotum. The external rings are about four inches (ca. 10 cm.) long, and are two and a half to three inches (6 to 8 cm.) apart. In animals in good condition there is a large mass of fat above the neck of the scrotum, between the spermatic cords. The mesorchium extends to the bottom of the tunica vaginalis forming a narrow fold (ca. 1 cm. wide) which attaches the epididymis to the posterior part of the tunic.
The inguinal canal presents several special features in the bull. The internal ring is very long. Its anterior border, formed by the edge of the internal oblique, is decidedly concave and is tendinous in its inner part. The long axis of the external ring is directed outward, forward, and downward. The spermatic cord lies in its outer part, the external pudic vessels in its middle. A muscular band about an inch wide, detached from the internal oblique muscle, crosses the outer side of the vaginal ring.
The vas deferens is small in caliber. The urogenital fold is narrow, so that the vasa are closer together in it than in the horse. On reaching the posterior part of the bladder they are in apposition for a distance of about four inches (10 cm.), flanked and overlapped by the vesiculæ seminales. They form ampullæ about four or five inches (10 to 12 cm.) long and half an inch (1.2 to 1.5 cm.) wide, the mucous lining of which is plicated. They then pass under the body of the prostate and unite with the ducts of the vesiculæ seminales to form the ejaculatory ducts. The latter have slit-like openings on either side of the colliculus seminalis.
The vesiculæ seminales are not bladder-like sacs, as in the horse, but are compact glandular organs with a lobulated surface. In the adult they measure about four or five inches (ca. 10 to 12 cm.) in length, two inches (5 cm.) in width in their largest part, and an inch or more (ca. 3 cm.) in thickness. The dorsal surface of each faces upward and inward and is partially covered with peritoneum. The ventral surface faces in the opposite direction and is non-peritoneal. Each may be regarded as consisting of a very thick-walled, sacculated tube, bent on itself in a tortuous manner. This tube, if straightened out, would be about ten inches (25 cm.) in length. They are commonly unsymmetrical in size and shape. Short branches are often given off from the chief tube. The excretory duct or neck joins the outer side of the vas deferens at an acute angle to form the ejaculatory duct.
Fig. 401.—Anterior Extremity of Penis of Bull, Left View. (After Böhm.)
Fig. 402.—Cross-section of Pelvic Urethra of Bull.
1, Prostate gland (pars disseminata); 2, urethra; 3, urethral muscle; 4, aponeurosis. The lumen of the urethra is black.
The structure of the vesicula is masked by a thick capsule of fibrous tissue and unstriped muscle, which maintains it in its bent condition and also sends trabeculæ between the alveoli. There is a central canal into which the secretion formed in the alveoli passes. The cavities (central canal and alveoli) are lined with columnar epithelium. On account of this structure the term glandulæ vesiculares is preferred by some anatomists.
The prostate is pale yellow in color, and consists of two parts. The body (Corpus prostatæ) is a mass which stretches across the dorsal surface of the neck of the bladder and the origin of the urethra. It measures about an inch and a half (ca. 3.5 to 4 cm.) transversely, and about half an inch (ca. 1 to 1.5 cm.) in width and thickness. The pars disseminata surrounds the pelvic part of the urethra; dorsally it forms a layer about half an inch (ca. 10 to 12 mm.) thick, but ventrally it is quite thin. It is concealed by the urethral (Wilson’s) muscle; hence it often escapes notice, but is very evident on cross-section (fig. 402). The prostatic ducts open into the urethra in rows between two folds of the mucous membrane which proceed backward from the colliculus seminalis.
The uterus masculinus appears to be absent frequently. Ellenberger states that it opens between the ejaculatory ducts, while Martin says that it usually has two orifices at the colliculus, but that it often unites with the vasa deferentia.
The bulbo-urethral (Cowper’s) glands are somewhat smaller than in the stallion. They are liable to escape notice, since they are covered by a thick layer of dense fibrous tissue and also partially by the bulbo-cavernosus muscle. Each has a single duct which opens into the urethra under cover of a fold of the mucous membrane.
The penis is cylindrical, and is longer and of very much smaller diameter than in the horse. Just behind the scrotum it forms an S-shaped curve, the sigmoid flexure; thus about one foot is folded up when the penis is fully retracted. The flexure is effaced during erection. The glans penis is about three inches (ca. 8 cm.) in length. It is flattened dorso-ventrally, and its extremity is pointed and twisted. The external urethral orifice is situated at the end of a groove formed by this twist; it is only large enough to admit a probe of medium size. Even in the non-erect state the penis is remarkably dense and firm. The tunica albuginea is very thick, and incloses the urethra. In the first part, as far as the first curve, there is a thick median septum penis. Beyond this there is a central axial rod of dense fibrous tissue from which numerous strong trabeculæ radiate. The erectile tissue is small in amount, so that the organ undergoes very little enlargement in erection.
The length of the penis in the adult is about three feet (ca. 90 cm.). The crura are flattened laterally. The suspensory ligaments are attached to the ventral ridge on the symphysis. The body is somewhat flattened dorso-ventrally beyond the first curve. The extremity of the glans is unsymmetrical, the urethral orifice being situated ventro-laterally. The glans contains little erectile tissue, and hence undergoes little enlargement in erection.
The bulbo-cavernosus muscle presents several remarkable features. It is for the greater part an inch or more (ca. 3 cm.) in thickness, but its length is only six to eight inches (15 to 20 cm.). It is covered by a strong aponeurosis, and is divided by a median raphé into two lateral halves except at its origin. It diminishes in size from behind forward, and its anterior extremity is pointed.
The ischio-cavernosus muscle resembles in general that of the horse, but is flattened laterally. It is covered by a close aponeurosis.
The retractor penis muscle resembles that of the horse in origin. Its two parts are about an inch (ca. 2 to 5 cm.) apart on the root of the penis, where they lie in a groove on either side of the bulbo-cavernosus. They then come close together and pass on either side of the ventral curve of the sigmoid flexure. Further forward they lie along the ventral aspect of the penis, and end about five or six inches (ca. 12 to 15 cm.) behind the glans.
The prepuce is very long and narrow. Its orifice is about two inches (ca. 5 cm.) behind the umbilicus; it is only large enough to admit a finger readily, and is surrounded by long hairs. The cavity of the sheath is about fifteen inches (35 to 40 cm.) long, and a little over an inch (ca. 3 cm.) in diameter. The lining membrane forms longitudinal folds; it is covered with squamous stratified epithelium, and has coiled tubular glands. The penile layer is glandless, and is reddish in color. It presents lymph nodules in its posterior part.
There are two pairs of preputial muscles which are derivatives of the panniculus carnosus. The anterior pair, the protractors of the prepuce (Mm. præputiales craniales), are two flat bands, two inches or more (5 to 6 cm.) in width, which arise close together in the xiphoid region, about eight inches (20 cm.) in front of the preputial orifice. Traced backward they diverge, leaving the umbilicus and an area about one and a half inches wide free, and then unite behind the preputial orifice. They draw the prepuce forward. The posterior pair, the retractors of the prepuce (Mm. præputiales caudales), arise in the inguinal region and converge on the anterior part of the prepuce. They draw the prepuce backward.
These muscles are subject to a good deal of variation. The retractor may be absent. Many fibers come in from the panniculus on either side, dip under the protractor, and are inserted into the skin just behind the preputial opening. The homologue of the protractor is present in the cow.
The urethra in its pelvic part is about five inches (12 cm.) long, and is of relatively small and uniform caliber. The urethral (Wilson’s) muscle incloses the tube ventrally and laterally; it is very thick, crescentic in cross-section, and is covered by an aponeurosis. Dorsally, the aponeurosis is thick and the muscle absent. Inside of these the pars disseminata of the prostate surrounds the urethra as far back as the bulbo-urethral glands. The colliculus seminalis is short, but prominent; from it the urethral crest extends forward to the trigonum vesicæ. The extrapelvic part has an enlargement, the bulb, at its origin; it then gradually diminishes in diameter, and is relatively very small at its termination. Other features have been mentioned in preceding paragraphs.
Fig. 403.—Anterior Part of Penis of Ram.
A, Right side; B, left side. (After Böhm.)
In the ram the urethra lies in a groove on the ventral surface of the corpus cavernosum. Its terminal part projects commonly 3 to 4 cm. beyond the glans penis, forming a twisted processus urethræ.
MALE GENITAL ORGANS OF THE PIG
The scrotum is situated a short distance from the anus, and is not so sharply defined from the surrounding parts as in the other animals.
The testicles are very large and are soft in texture. Their long axis is almost vertical, the free border being posterior and the tail of the epididymis dorsal. The mediastinum testis is well developed. The epididymis is closely attached to the testicle and the tunica vaginalis; the tail is specially large.
The spermatic cord is necessarily very long (20 to 25 cm. in a boar of medium size). The vas deferens in its testicular part is flexuous, and is closely attached to the tunica vaginalis; it forms no ampullæ. The cremaster externus is well developed, and extends to about the middle of the scrotal part of the tunic.
The vesiculæ seminales are exceedingly large, and extend into the abdominal cavity. They are three-sided pyramidal masses, are in apposition with each other medially, and cover the posterior part of the bladder and the ureters, the vasa deferentia, the body of the prostate, and the anterior part of the urethra. They are pale pink in color, distinctly lobulated and glandular in structure, and contain large alveoli, but no central cavity. There are two excretory ducts which open into the urethra close to the vasa deferentia; the two ducts frequently unite.
In the adult boar the vesiculæ are about five to six inches (ca. 12 to 15 cm.) long, two to three inches (ca. 5 to 8 cm.) wide, and one and a half to two inches (ca. 4 to 5 cm.) thick; they weigh about 6 to 8 ounces each.
The prostate consists of two parts, as in the ox. The body is about an inch (2.5 cm.) wide, and embraces the neck of the bladder and the urethra at their junction dorsally and laterally. It is concealed by the vesiculæ seminales. The pars disseminata forms a layer which surrounds the pelvic part of the urethra, and is covered by the urethral muscle.
The uterus masculinus is small.
The bulbo-urethral (Cowper’s) glands are very large and dense. They are somewhat cylindrical, and lie on either side of and upon the posterior two-thirds of the pelvic urethra. In a large boar they are about five inches (ca. 12 cm.) in length and an inch or more (ca. 2.5 to 3 cm.) in diameter. They are partially covered with a layer of striated muscle (M. ischio-glandularis), and have a lobulated surface. Each gland has a large excretory duct which leaves at the posterior extremity, perforates the dorsal wall of the urethra at the ischial arch, and opens in a cul-de-sac covered by a fold of mucous membrane.
Fig. 404.—Genital Organs of Boar.
a, Testicle; b, epididymis; c, vas deferens; d, spermatic artery; e, vesicula seminalis reflected to show the body of the prostate, f; e′, excretory ducts of vesiculæ; g, bulbo-urethral (Cowper’s) gland; h, urinary bladder; i, urethral muscle; k, bulbo-cavernosus muscle; l, penis; l′, sigmoid flexure of penis; l″, spiral anterior part of penis, exposed by slitting open prepuce; m, orifice of preputial pouch; n, retractor penis muscle. (Ellenberger-Baum, Anat. d. Haustiere.)
It is to be noted that these accessory glands are very small in animals which have been castrated early.
The penis resembles in general that of the ox. The sigmoid flexure is, however, prescrotal. The anterior portion has no glans, and is spirally twisted, especially in erection. The urethral orifice is slit-like and is situated ventro-laterally, close to the pointed extremity. The penis in the adult boar measures about 18 to 20 inches (ca. 45 to 50 cm.) in length. Its muscles resemble those of the bull; the bulbo-cavernosus is very strong but short.
The prepuce has a narrow orifice, around which there are a number of stiff hairs. The cavity is partially divided by a circular fold into a posterior narrow portion and a much wider anterior portion. The lining membrane of the posterior part is papillated, and is in close contact with the penis. In the dorsal wall of the wide part there is a circular opening which leads into a cul-de-sac, the preputial diverticulum. This pouch is ovoid in form (when distended), and varies greatly in size in different subjects. It extends for the most part backward over the narrow part of the prepuce. Its cavity is partially divided by a narrow median septum. It contains usually decomposing urine and macerated epithelium, which have a characteristic and very unpleasant odor. Concrements have been found in it.
Oehmke found that a cast of the pouch in a Yorkshire boar weighing about 500 pounds measured 9 cm. in length, 12½ cm. in breadth, and 6 cm. in height. The opening into the prepuce will admit two fingers in the adult, but is ordinarily closed by folds of the lining membrane. The sac is much smaller in animals which were castrated young, and the opening is vertical and further back; in them it is often empty or contains only a little clear urine. The pouch is covered by a layer of striped muscle which is mainly derived from the homologue of the protractor of the prepuce of ruminants.
The urethra has a very long pelvic portion (ca. 15 to 18 cm. long in the adult); it is inclosed (with the pars disseminata of the prostate) by a thick urethral muscle. There is a distinct bulb at the root of the penis. The penile part is of small caliber, and is surrounded by erectile tissue which, however, does not extend to the extremity of the penis.
MALE GENITAL ORGANS OF THE DOG
The scrotum is situated about half-way between the inguinal region and the anus. The skin covering it is pigmented and is covered sparsely with fine hairs. The raphé is not very distinct.
The testicles are relatively small, and have a round-oval form. The long axis is oblique, and is directed upward and backward. The mediastinum testis is central and is well developed. The epididymis is large, and is closely attached along the outer part of the dorsal border of the testicle.
The spermatic cord and the tunica vaginalis are long; they cross the side of the penis very obliquely. The upper end of the tunic is sometimes closed, so that there is then no vaginal ring. The vasa deferentia have very narrow ampullæ.
The vesiculæ seminales are absent; hence there are no ejaculatory ducts.
The prostate is relatively large; it is yellowish in color, dense in structure, and lies at the anterior border of the pubis. It is globular, and surrounds the neck of the bladder and the urethra at their junction. A faint median furrow indicates a division into two lateral lobes. The capsule and stroma contain a large amount of unstriped muscle. The ducts are numerous. Lobules of prostatic tissue (pars disseminata) are also found on the urethra further back. The gland is subject to much variation in size, and is often enlarged, especially in old subjects.
The uterus masculinus is a very small saccule (Utriculus prostaticus), often difficult to find.
The bulbo-urethral (Cowper’s) glands are absent.
The penis presents several special features. In its posterior part there are two distinct corpora cavernosa, separated by a median septum penis. In its anterior part there is a bone, the os penis, which in large dogs reaches a length of four inches (ca. 10 cm.) or more. It is regarded as a continuation forward of the corpus cavernosum. Ventrally it is grooved for the urethra; dorsally it is convex, and anteriorly it becomes smaller and has a curved fibrous prolongation. The glans penis is very long, extending over the entire length of the os penis; posteriorly it forms a rounded enlargement, the bulbus glandis; anteriorly it is cylindrical, smaller, and pointed at the extremity. Just in front of the bulbus glandis there is a thick circular layer of glands, forming the annulus glandularis (Schmaltz). The two dorsal veins arise from the bulbus glandis, pass backward on the dorsum penis, and unite at the ischial arch. A small muscle (M. compressor venæ dorsalis penis) arises from the tuber ischii on either side; the two converge on the dorsum penis near the bulbus glandis. They compress the dorsal veins, and may also tend to elevate the penis and thus assist in copulation. The other muscles offer no features worthy of special description.
The prepuce forms a complete sheath around the anterior part of the penis. The outer layer is ordinary integument. The inner layer has the character of a glandular mucous membrane; it is thin and reddish in color. The penile layer is glandless. In the fundus of the præputial cavity there are numerous lymph follicles. The protractor muscles arise in the xiphoid region and decussate posteriorly around the extremity of the penis.
Fig. 405.—External Genital Organs of Male Dog, Ventro-lateral View of Preparation.
1, Scrotum; 1′, tunica vaginalis; 2, epididymis; 3, vascular part of spermatic cord; 4, vas deferens; 5, prepuce; 6, glans penis; 6′, corpus cavernosum penis; 7, bulbus glandis; 7′, contour of bulbus in erection; 8, ischio-cavernosus muscle; a, acetabulum; b, obturator foramen. (After Ellenberger, in Leisering’s Atlas.)
Fig. 406.—Internal Genital Organs of Male Dog.
1, Urinary bladder; 2, ureter; 3, vas deferens; 4, prostate; 5, urethral muscle; 6, bulb of urethra; a, abdominal wall; b, ilium; c, ischium. (After Ellenberger, in Leisering’s Atlas.)
The pelvic part of the urethra is relatively long. Its first part is inclosed in the prostate.[148] At the ischial arch the urethra has a well-developed bilobed bulb, formed by an enlargement here of the corpus spongiosum. It is covered by the strong but short bulbo-cavernosus muscle. The other erectile bodies have been described.
The urethral (Wilson’s) muscle is very strong; it encircles the urethra and has a median raphé dorsally.
THE FEMALE GENITAL ORGANS
The female genital organs (Organa genitalia feminina) are: (1) The two ovaries, the essential reproductive glands, in which the ova are produced; (2) the uterine or Fallopian tubes, which convey the ova to the uterus; (3) the uterus, in which the ovum develops; (4) the vagina, a dilatable passage through which the fœtus is expelled from the uterus; (5) the vulva, the terminal segment of the genital tract, which serves also for the expulsion of the urine; (6) the mammary glands, which are glands of the skin, but are so closely associated functionally with the generative organs proper as to be described with them.
GENITAL ORGANS OF THE MARE
THE OVARIES
Fig. 407.—Lateral View of Genital Organs and Adjacent Structures of Mare.
The removal of the other abdominal viscera has allowed the ovaries and uterus to sink down, whereas they are normally in contact with the roof of the cavity in the non-pregnant subject. 1, Left ovary; 2, Fallopian tube; 3, left cornu uteri; 4, right cornu uteri; 5, corpus uteri; 5′, portio vaginalis uteri, and 5″, os uteri, seen through window cut in vagina; 6, broad ligament of uterus; 6″, round ligament; 7, vagina; 8, labia vulvæ; 9, rima vulvæ; 9′ superior commissure, and 9′, inferior commissure of vulva; 10, constrictor vulvæ; 11, position of vestibular bulb; 12, ventral wall of abdomen; 13, left kidney; 14, left ureter; 15, urinary bladder; 16, urethra; 17, rectum; 18, anus; 19, 19′, unpaired and paired parts of sphincter ani externus; 20, retractor ani cut at disappearance under sphincter; 21, suspensory ligament of anus; 22, longitudinal muscular layer of rectum; 22′, recto-coccygeus; 23, constrictor vaginæ; a, utero-ovarian artery, with ovarian (a′) and uterine (a″) branches; b, uterine artery; c, umbilical artery; d, ischium; e, pubis; f, ilium. (After Ellenberger, in Leisering’s Atlas.)
The ovaries (Ovaria) of the mare are bean-shaped, and are much smaller than the testicles. Their size varies much in different subjects, and they are normally larger in young than in old animals; one ovary is often larger than the other. They are about three inches (ca. 7 to 8 cm.) long and an inch to an inch and a half (ca. 3 to 4 cm.) thick. The weight is about two and a half to three ounces (ca. 70 to 80 grams).
Each presents for description two surfaces, two borders, and two extremities or poles. The surfaces are termed internal and external (Facies medialis, lateralis); they are both smooth and rounded.[149] The attached or mesovarial border (Margo mesovaricus) is convex. It is inclosed in a part of the broad ligament termed the mesovarium; the vessels and nerves reach the gland at this border. The free border (Margo liber) is marked by a notch which leads into a depression, the ovulation fossa. The tubal or anterior extremity (Extremitas tubaria) is rounded, and is related to the fimbriated end of the uterine or Fallopian tube. The uterine or posterior extremity (Extremitas uterina) is also round, and is connected with the horn of the uterus by the ovarian ligament.
The ovaries are situated in the sublumbar region of the abdominal cavity, about a handbreadth behind the corresponding kidney. They are in contact with the lumbar wall of the abdomen, and are commonly about two or three inches (ca. 5 to 7.5 cm.) from the median plane. The distance from the ovaries to the vulvar orifice is about twenty inches (ca. 50 cm.) in a mare of medium size. The attached (mesovarial) border is commonly directed toward the median plane, the free border laterally and somewhat ventrally.
The position of the ovaries is not constant, but is subject to less variation than might be expected from their mode of attachment. The normal variations in the non-pregnant state are chiefly in a transverse direction, and do not usually exceed two or three inches (ca. 5 to 7 cm.). It is not at all rare to find the ovary deflected medially, so that the external surface faces ventrally. In the longitudinal direction little variation appears to occur. The right ovary is usually about four or five inches (ca. 10 to 12 cm.), and the left one about three or four inches (ca. 8 to 10 cm.), behind the corresponding kidney. Thus they lie about in a transverse plane tangent to the external angles of the ilia, i. e., through the fifth lumbar vertebra. They may be about two inches (ca. 5 cm.) from the extremity of the corresponding cornu of the uterus or in contact with it. The right ovary commonly lies a little (ca. 2.5 cm.) further forward than the left one. Except during pregnancy, they are normally in contact with the lumbar abdominal wall, and do not hang down among the adjacent viscera.
Fig. 408.—Right Ovary of Mare, with Adjacent Structures.
The extremity of the cornu uteri is opened. 1, Ovary; 2, Fallopian tube, with its ostium abdominale (2′), fimbriæ (2″), and ostium uterinum (2‴); 3, cornu uteri, with its mucous lining (3′); 4, ovarian ligament; 4′, mesosalpinx. (After Ellenberger, in Leisering’s Atlas, reduced.)
The ovary is attached to the sublumbar region by the anterior part of the broad ligament; this part of the ligament, the mesovarium, is about three or four inches (ca. 8 to 10 cm.) wide, measured from the ovary directly to the parietal attachment. The uterine or posterior extremity of the ovary, is connected with the extremity of the cornu of the uterus by the ovarian ligament (Ligamentum ovarii proprium); this is a band of unstriped muscle inclosed between the layers of the broad ligament.
Structure.—The greater part of the surface of the ovary has a covering of peritoneum. The peritoneal investment is absent at the attached border where the vessels and nerves enter; this area is termed the hilus. The ovulation fossa is covered by a layer of columnar cells, a remnant of the primitive germinal epithelium. The stroma of the ovary (Stroma ovarii) is a network of connective tissue and unstriped muscular fibers. In the deeper or medullary portion of the stroma (Zona vasculosa) the meshes are largely occupied by the numerous blood-vessels. In the peripheral or cortical portion (Zona parenchymatosa) are numerous ova (Ovula) in various stages of development. The immature ova are surrounded by follicle cells; those more advanced in development are inclosed also by a condensation of the stroma termed the theca folliculi; within the theca is a quantity of fluid, the liquor folliculi. These constitute the Graafian follicles (Folliculi oöphori), which enlarge as they mature, becoming visible to the naked eye as vesicles with a diameter of a centimeter or more. When fully developed, the follicles are superficially situated, and often project slightly from the surface of the ovary. At intervals follicles rupture and their contents escape. This process, which sets free the ovum, is termed ovulation; it takes place in the mare only at the ovulation fossa, and occurs during the periods of œstrum.
Fig. 409.—Schematic Representation of Changes in Ovary of Mare from Fœtal to Adult State. (After Born.)
The changes affect chiefly the free border (upper in figure) and the extent and form of the area covered by germinal epithelium (4). 1, Peritoneum (broad ligament); 2, ligament of ovary; 3, fimbria of Fallopian tube; 4, germinal epithelium; 5, vessels, which reach the ovary at the attached border (6). The latter represents the hilus, while the deep depression at the free border is the ovulation fossa. (Ellenberger, in Leisering’s Atlas.)
After rupture of a follicle its cavity is partly occupied by a blood-clot, constituting what may be termed a corpus rubrum. By proliferation and enlargement and fatty changes, the follicle cells are transformed into lutein cells, forming a yellow mass known as a corpus luteum. If impregnation takes place, the accompanying increase in vascularity of the organs may cause the corpus luteum to reach a large size; if impregnation does not occur, it is much smaller, and is sooner replaced by scar tissue, the corpus albicans.
In the young foal the ovaries are large and oval in form. The free border is convex and is covered by germinal epithelium, which extends over part of the surfaces also. This area is distinguishable by its dull gray appearance from the peritoneal surface, which has the usual smooth glistening character. As growth proceeds the ovary gradually becomes bent until it assumes its definitive curved shape. The germinal epithelium is then limited to the ovulation fossa. The ovary migrates somewhat during development from its primitive position, which is the same as that of the testicle.
In old animals the ovaries commonly consist largely of fibrous tissue, in which there are often cysts of various sizes. The ova, present in enormous number at birth, have then been extruded, or destroyed by phagocytic action or degeneration.
Vessels and Nerves.—The arteries of the ovary are derived from the ovarian artery. The artery is relatively large and is flexuous; it reaches the attached border of the ovary by passing between the layers of the mesovarium. The veins are large and numerous. They form a plexus somewhat like that of the spermatic cord. The lymph vessels pass to the lumbar glands. The nerves are derived from the sympathetic system through the renal and aortic plexuses. They accompany the arterial branches.
THE UTERINE OR FALLOPIAN TUBES
The uterine or Fallopian tubes (Tubæ uterinæ) act as excretory ducts of the ovaries, since they convey the ova from the reproductive glands to the uterus. They are not, however, in direct continuity with the glands, but rather partly in contiguity with, and partly attached to, them.[150] They are two flexuous tubes, about ten to twelve inches (ca. 25 to 30 cm.) long, which extend from the extremities of the uterine cornua to the ovaries. Each is inclosed in a peritoneal fold, derived from the external layer of the broad ligament, and termed the mesosalpinx. This largely covers the outer aspect of the ovary, and forms with it and the broad ligament a pouch called the bursa ovarica. The uterine extremity of the tube communicates with the cavity of the cornu by a minute orifice, the ostium uterinum. The ovarian or fimbriated extremity is expanded into a funnel-shaped infundibulum. The margin of the latter is slit into irregular processes or fimbriæ, some of which, the fimbriæ ovaricæ, are attached in the ovulation fossa. In the center of the fimbriated extremity is a small opening, the ostium abdominale, by which the tube communicates with the peritoneal cavity. The tube appears normally to be applied to the ovary, so that the extruded ova pass into it and are conveyed to the uterus.[151]
Pedunculated cysts, the hydatids of Morgagni, are often found on one or more of the fimbriæ. In the mesosalpinx are blind flexuous tubules, which constitute the paroöphoron, a remnant of the Wolffian body. They are most evident in the young adult, and tend to disappear with increasing age. Not uncommonly they give rise to cysts.
Structure.—The tube is covered externally by a serous coat formed by the mesosalpinx. The serous membrane is continued on the fimbriæ, and meets the mucous lining on them. The fibrous coat or adventitia is continuous with the fibrous lamina of the broad ligament. The muscular coat consists chiefly of circular fibers, although longitudinal fibers occur externally. The mucous coat is thin and is much plicated. The folds (Plicæ tubariæ) are chiefly longitudinal, but in the wide part of the tube (Ampullæ tubæ) they are very complex, so that on cross-sections the spaces between the folds may be mistaken for branched tubular glands. The folds are continued on to the fimbriæ. The epithelium is a single layer of columnar ciliated cells, the cilia producing a current directed toward the uterus. At the fimbriated extremity this epithelium passes gradually into the squamous type of the serous coat.
Vessels and Nerves.—The arteries are derived from the utero-ovarian artery. The veins are satellites of the arteries. The lymphatics pass with the ovarian vessels to the lumbar glands. The nerves have a similar origin to those of the ovary.
THE UTERUS
The uterus is a hollow muscular organ, which receives the Fallopian tubes anteriorly and opens into the vagina posteriorly. It is situated chiefly in the abdominal cavity, but extends a short distance into the pelvic cavity. It is attached to the lumbar wall of the abdomen and the lateral walls of the pelvic cavity by two folds of peritoneum termed the broad ligaments. It consists of two cornua or horns, the body, and the neck.
The cornua or horns of the uterus (Cornua uteri) are situated entirely in the abdomen. They appear to vary considerably in position; commonly they are pressed up against the sublumbar muscles by the intestine (left portions of large colon, small colon, and small intestine). They are cylindrical, and are about ten inches (ca. 25 cm.) in length. The anterior extremity of each forms a blunt point which receives the Fallopian tube. Posteriorly they increase somewhat in caliber, converge, and unite with the body. The dorsal (or attached) border is slightly concave and is attached to the broad ligament. The ventral border is convex and free.