Fig. 66.—Frontal Section of Left Femur of Horse, Anterior View.
The figure shows that the medullary cavity is traversed for the most part by fine bony trabeculæ.
The distal extremity (Extremitas distalis) is large in both directions and comprises the trochlea in front and two condyles behind. The trochlea consists of two ridges separated by a groove, and forms an extensive surface (Facies patellaris) for articulation with the patella. It is very unsymmetrical; the inner ridge or lip is much wider, more prominent, and extends up higher than the external one, and the two converge below. The condyles, internal and external (Condylus medialis, lateralis), are separated by the deep intercondyloid fossa (Fossa intercondyloidea), and articulate with the condyles of the tibia and the semilunar cartilages of the stifle joint. A ridge connects each condyle with the lower part of the corresponding lip of the trochlea. The intercondyloid fossa lodges the spine of the tibia and the crucial ligaments of the stifle joint, which are attached here.
The condyles are obliquely placed, with their long axes directed downward, forward, and inward. The articular surface of the external condyle is more strongly convex from side to side than that of the inner one, and the ridge which connects it with the trochlea is much narrower.
The internal epicondyle (Epicondylus medialis) is a rounded prominence on the internal surface of the internal condyle, to which the internal lateral ligament and the adductor muscle are attached. The corresponding external epicondyle (Epicondylus lateralis) is less distinct; it presents a mark where the lateral ligament is attached, below and behind which there is a depression (Fossa musculi poplitei) in which the popliteus muscle arises. Between the external condyle and trochlea is the extensor fossa (Fossa extensoria), in which the tendon of origin of the anterior extensor and peroneus tertius is attached.
Development.—The shaft and the distal end each ossify from one center, but the proximal end has two centers, one of which is for the great trochanter. The edge of the external trochanter also has a separate center. The proximal end fuses with the shaft at three to three and a half years, the distal at about three and a half years.
Fig. 67.—Distal Extremity of Right Femur of Horse, End View.
THE TIBIA
The tibia is a long bone which extends obliquely downward and backward from the stifle to the hock. It articulates above with the femur, below with the tarsus, and externally with the fibula. It possesses a shaft and two extremities.
The shaft or body (Corpus tibiæ), large and three-sided above, becomes smaller and flattened in the sagittal direction below, but widens a little at the distal end. It presents for notice three surfaces and three borders. The internal surface (Facies medialis) is broad above, where it furnishes insertion to the internal lateral ligament and the sartorius and gracilis muscles; below this it is convex and subcutaneous. The external surface (Facies lateralis) is smooth and somewhat spiral. It is wide and concave in its upper part, below which it becomes narrower and slightly convex, and winds gradually to the front of the bone; near the distal end it widens a little, becomes flat, and faces forward. The posterior surface (Facies posterior) is flattened, and is divided into two parts by the rough popliteal line, which runs obliquely from the upper part of the external border to the middle of the internal border. The triangular area above the line is occupied by the popliteus muscle, while the area below is marked by rough lines (Lineæ musculares) to which the deep flexor muscle of the digit is attached; the lines fade out below, where the surface is smooth and flat. The nutrient foramen is situated on or near the popliteal line. The anterior border is very prominent in its upper third, forming the tibial crest (Crista tibiæ); below it is reduced to a rough line, which ends at a small elevation near the distal end of the bone. The internal border (Margo medialis) is rounded in its upper half, to which the popliteus muscle is attached, and a tubercle is found on this part. The lower part is a rough line on well-marked bones. The external border (Crista interossea) is concave in its upper part and concurs with the fibula in the formation of the interosseous space of the leg; a smooth impression indicates the course of the anterior tibial vessels through the space to the front of the leg. Lower down the border divides and incloses a narrow triangular surface.
Fig. 68.—Right Tibia and Fibula of Horse, External View.
The proximal extremity (Extremitas proximalis) is large and three-sided. It bears two lateral eminences, the internal and external condyles (Condylus medialis, lateralis). Each presents a somewhat saddle-shaped surface for articulation with the condyle of the femur and the semilunar cartilage. The spine or intercondyloid eminence (Eminentia intercondyloidea) is the central prominence, upon which the articular surfaces are continued; it consists of a high inner part and a lower outer part (Tuberculum intercondyloideum mediale, laterale). On, before, and behind the spine are the anterior and posterior intercondyloid fossæ, in which the anterior crucial ligament and the semilunar cartilages are attached. The condyles are separated behind by the deep popliteal notch (Incisura poplitea), on the inner side of which is a tubercle for the attachment of the posterior crucial ligament. The external condyle has an overhanging outer margin, below which is a facet for articulation with the fibula. The large anterior eminence is the tuberosity of the tibia (Tuberositas tibiæ). It is marked in front by a groove, the lower part of which gives attachment to the middle patellar ligament, and the groove is flanked by rough areas for the attachment of the internal and external patellar ligaments. A semicircular smooth notch (Sulcus muscularis) separates the tuberosity from the external condyle, and gives passage to the tendon of origin of the anterior extensor and the peroneus tertius.
Fig. 69.—Right Tibia and Fibula of Horse, Posterior View.
The distal extremity (Extremitas distalis) is much smaller than the proximal; it is quadrangular in form and larger internally than externally. It presents an articular surface (Cochlea tibiæ), which is adapted to the trochlea of the tibial tarsal bone (astragalus), and consists of two grooves separated by a ridge. The ridge and grooves are directed obliquely forward and outward, and are bounded laterally by the malleoli, to which the lateral ligaments of the hock joint are attached. The internal malleolus (Malleolus tibialis) is the more prominent of the two, and forms the anterior boundary of a groove for the tendon of the inner head of the flexor perforans. The external malleolus (Malleolus fibularis) is broader, and is marked by a vertical groove for the passage of the lateral extensor tendon.
Fig. 70.—Right Tibia and Fibula of Horse, Anterior View.
Development.—The tibia has the usual three chief centers of ossification and supplementary ones for the tuberosity and the external malleolus. The latter is really the distal end of the fibula; it is a separate piece at birth, and the line of union is commonly quite evident in the adult in the external articular groove. The proximal end unites with the shaft at about three and a half years, and the distal end at about two years of age.
THE FIBULA
The fibula of the horse is a much reduced long bone, situated along the outer side of the tibia.
The shaft or body (Corpus fibulæ) is a slender rod which forms the outer boundary of the interosseous space; it usually terminates below in a pointed end about one-half to two-thirds of the way down the external border of the tibia.
The proximal extremity or head (Capitulum fibulæ) is relatively large, and is flattened transversely. Its internal surface presents a narrow area along the upper border for articulation with the tibia. The external surface is rough and gives attachment to the external lateral ligament of the stifle joint. It has rounded anterior and posterior borders.
Fig. 71.—Proximal Extremity of Right Tibia of Horse, End View.
l.c.a., l.c.p., Depressions for attachment of anterior and posterior crucial ligaments; l, m, m, depressions for attachment of semilunar cartilages.
The distal extremity is fused with the tibia, constituting the external malleolus.
Development.—This resembles that of the ulna. The embryonic cartilaginous fibula extends the entire length of the leg, but does not articulate with the femur. The lower part of the shaft is usually reduced to a fibrous band. Three centers of ossification appear, one each for the shaft and the extremities. The distal end unites early with the tibia, forming the external malleolus.
It is interesting to note that in some cases the entire shaft of the fibula develops, a reversion to the condition in the Miocene ancestors of the present horse.
THE PATELLA
The patella is a large sesamoid bone which articulates with the trochlea of the femur. It presents for description two surfaces, two borders, a base, and an apex.
The anterior or free surface (Facies libera) is irregularly quadrilateral, convex, and rough for muscular and ligamentous attachment.
The posterior or articular surface is smaller and is triangular in outline. It presents a vertical rounded ridge, which corresponds to the groove on the trochlea of the femur, and separates two concave areas. Of the latter, the inner cavity is much the larger, and is not very well adapted to the inner lip of the trochlea; in the fresh state, however, it is completed and rendered more congruent by the curved accessory fibro-cartilage.
Fig. 72.—Frontal Section of Right Tibia of Horse, Anterior View.
The lateral borders converge to the apex below, and each forms a prominence or angle at the base. The inner angle and the adjacent part of the border give attachment to the fibro-cartilage of the patella, which increases the articular surface. The external border is rounded and its angle is less prominent.
The base (Basis patellæ) faces upward and backward, and is convex transversely, concave from before backward.
The apex forms a blunt point directed downward.
Development.—The patella develops as a sesamoid bone from a single center in a cartilaginous deposit in the tendon of the quadriceps femoris muscle.
THE TARSUS
The tarsus or hock of the horse usually comprises six short bones (Ossa tarsi), but exceptionally seven are present.
The Tibial Tarsal Bone
The tibial tarsal bone (Os tarsi tibiale, astragalus, or talus) is the inner bone of the proximal row. It is extremely irregular in form, but may be considered as offering six surfaces for description.
Fig. 73.—Right Patella of Horse, Anterior View.
Fig. 74.—Right Patella of Horse, Posterior View.
The superior and the anterior or dorsal surface are continuous, and form a trochlea for articulation with the distal end of the tibia. The trochlea consists of two oblique ridges with a deep groove between them, which curve spirally forward, downward, and outward. There is usually a shallow synovial fossa in the groove. The inferior surface is convex from before backward, and most of it articulates with the central tarsal; externally it has an oblique facet for the fourth tarsal, and a non-articular groove cuts into the surface to its middle. The posterior or plantar surface is oblique and extremely irregular; it presents four facets for articulation with the fibular tarsal bone; the facets are separated by rough excavated areas, and the largest fossa (Sulcus tali) forms with a corresponding one on the fibular tarsal a cavity termed the sinus tarsi. The internal surface bears on its lower part a large tuberosity, and on its upper part a small one for the attachment of the internal lateral ligament. The external surface is smaller than the internal, and is marked by a wide rough fossa in which the external ligament is attached.
The Fibular Tarsal Bone
Fig. 75.—Right Tarsus and Upper Part of Metatarsus of Horse, Internal View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 76.—Right Tarsus and Upper Part of Metatarsus of Horse, Posterior (Plantar) View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
The fibular tarsal bone (Os tarsi fibulare, calcaneum, os calcis) is the largest bone of the hock. It is elongated, flattened from side to side, and forms a lever for the muscles which extend the hock joint. It consists of a body and an inner process, the sustentaculum tali.
Fig. 77.—Right Tibial Tarsal Bone of Horse, Anterior View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 78.—Right Tibial Tarsal Bone of Horse, External View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
The body (Corpus calcanei) is enlarged at its proximal end to form the tuber calcis or “point of the hock.” The posterior part of this eminence gives attachment to the tendon of the gastrocnemius, while in front and laterally it furnishes insertion to tendons of the flexor perforatus, biceps, and semitendinosus muscles. The inferior extremity bears a concave facet for articulation with the fourth tarsal bone. The internal surface has on its lower part a strong process, the sustentaculum tali, which projects inward. The process has a large, oval, slightly concave facet in front for articulation with the tibial tarsal, and sometimes a small articular surface below for the central tarsal bone. Its plantar surface forms with the smooth inner surface of the body a groove for the deep flexor tendon (Sulcus musculi flexoris hallucis longi). Its inner surface has a prominence on the lower part for the attachment of the lateral ligament. The external surface of the body is flattened, except below, where there is a rough prominence for the attachment of the lateral ligament. The anterior or dorsal border is concave in its length, smooth and rounded in its upper part. About its middle is a blunt-pointed projection (Processus cochlearis) which bears facets on its inner and lower surfaces for articulation with the tibial tarsal bone, and is roughened outwardly for ligamentous attachment. Below this are two facets for the tibial tarsal, and an extensive rough fossa which concurs in the formation of the sinus tarsi. The posterior or plantar border is straight and thick, and widens a little at either end; it is rough, and gives attachment to the long plantar ligament.
Fig. 79.—Right Fibular Tarsal Bone of Horse, Anterior View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 80.—Right Fourth Tarsal Bone of Horse, Upper Surface. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 81.—Right Central Tarsal Bone of Horse, Upper Surface. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 82.—Right First, Second, and Third Tarsal Bones of Horse, Upper Surface. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
Fig. 83.—Proximal Articular Surfaces of Left Metatarsal Bones of Horse. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
The Central Tarsal Bone
The central tarsal bone (Os tarsi centrale, scaphoid, or navicular) is irregularly quadrilateral, and is situated between the tibial tarsal above and the third tarsal below. It is flattened from above downward, and may be described as having two surfaces and four borders. The superior surface is concave from before backward, and almost all of it articulates with the tibial tarsal; a non-articular depression cuts into its outer part, and sometimes there is a facet for the fibular tarsal bone on the posterior angle. The inferior surface is convex, and is crossed by a non-articular groove, which separates facets for articulation with the third and the first and second (fused) tarsals. The anterior or dorsal border and the internal border are continuous, convex, and rough. The posterior or plantar border bears two prominences, separated by a notch. The external border is oblique, and bears anterior and posterior facets for articulation with the fourth tarsal, between which it is excavated and rough.
Fig. 84.—Right Tarsal and Metatarsal Bones of Horse. External View. (After Schmaltz, Atlas d. d. Anat. d. Pferdes.)
First and Second Tarsal Bones
The first and second tarsal bones (Os tarsale primum et secundum, cuneiform parvum) are usually fused in the horse, forming a bone of very irregular shape, situated in the inner and posterior part of the lower row, below the central and behind the third tarsal. It is the smallest of the tarsal bones, and may be described as having two surfaces, two borders, and two extremities. The internal surface faces backward and inward, and is convex. Its anterior part is ridged, and gives attachment to the internal lateral ligament, and its posterior part bears an imprint where the inner tendon of the tibialis anterior is inserted. The external surface is marked by a deep notch which indicates the division between the first and second tarsal elements; it bears on its anterior part a large concave facet for the central tarsal. The superior border is convex. The inferior border is broad in front, where it articulates with the large and inner small metatarsal bones. The anterior extremity has a small facet for articulation with the third tarsal, and bears internally a ridge or tubercle. The posterior extremity is a blunt point.
In some cases the first and second tarsal bones remain separate—a remarkable reversion to the condition in the early ancestors of the horse. In such specimens the first tarsal is a discoid bone, articulating above with the central, below with the small metacarpal bone. The second tarsal is quadrangular, equivalent to the thick anterior part of the bone as described above, and overlapped by the anterior part of the first tarsal.
The Third Tarsal Bone
The third tarsal bone (Os tarsale tertium, third or great cuneiform) resembles the central, but is smaller and triangular in outline. It is situated between the central above and the large metatarsal bone below. It possesses two surfaces and three borders.
The superior surface is concave, and is crossed by a non-articular depression which divides it into two unequal facets; it articulates with the central tarsal. The inferior surface is slightly convex, and rests on the large metatarsal bone; it has an extensive central rough excavation. The anterior or dorsal border is convex and bears a rounded ridge on its inner part. The internal border is deeply notched and has a small facet for the second tarsal on its anterior part. The external border is also divided by a notch into two parts, and bears two diagonally opposite facets for articulation with the fourth tarsal. In some cases there is a facet for the inner small metatarsal bone.
Fig. 85.—Cross-sections of Metacarpal and Metatarsal Bones of Horse. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
The Fourth Tarsal Bone
The fourth tarsal bone (Os tarsale quartum, cuboid) is the outer bone of the lower row, and is equal in height to the central and third together. It is cuboid in shape and presents six surfaces.
The superior surface is convex from side to side, and articulates chiefly with the fibular tarsal, but to a small extent with the tibial tarsal also. The inferior surface rests on the large and external small metatarsal bones. The internal surface bears four facets for articulation with the central and third tarsal bones. It is crossed from before backward by a smooth groove, which by apposition with the adjacent bones forms the canal of the tarsus (Canalis tarsi) for the passage of the perforating tarsal vessels. The anterior or dorsal, external, and posterior or plantar surfaces are continuous and rough. A tuberosity behind gives attachment to the plantar ligament.
Development.—The fibular tarsal bone has two centers of ossification, one for the main mass and the other for the tuber calcis; the latter fuses with the rest of the bone at about three years of age. The first and second tarsals have separate centers, but fusion usually occurs before birth. Each of the other bones ossifies from a single center.
Fig. 86.—Digital Bones of Fore Limb of Horse, Volar Aspect.
Fig. 87.—Digital Bones of Hind Limb of Horse, Volar Aspect.
THE METATARSUS
The metatarsal bones (Ossa metatarsalia), three in number, have the same general arrangement as the metacarpal bones, but present some important differences. Their direction is slightly oblique, downward and a little forward.
The large or third metatarsal bone is about one-sixth longer than the corresponding metacarpal; in an animal of medium size the difference is about two inches. The shaft is more cylindrical, and is almost circular on cross-section, except in its lower part. At the upper part of its external surface there is a groove, which is directed obliquely downward and backward, and is continued by the furrow formed by the apposition of the external metatarsal bone; it indicates the course of the great metatarsal artery. A faint impression in a similar place on the inner side marks the position of the corresponding vein. The nutrient foramen is relatively higher than on the metacarpal bone. The proximal extremity is much wider from before backward than that of the metacarpal bone. Its articular surface is slightly concave, and is marked by a large central non-articular depression, continued outward by a deep notch. The greater part of the surface articulates with the third tarsal, but there is an outer facet for the fourth, and usually a small facet posterointernally for the second tarsal bone. Posteriorly there are two pairs of facets for articulation with the small metatarsal bones. The front is crossed by a rough ridge for insertion, which becomes larger and turns downward on the outer side behind the vascular groove. The distal extremity closely resembles that of the corresponding metacarpal bone.
In some cases the lower part of the shaft is bent backward somewhat. The articular surface extends a little higher behind than in the case of the metacarpal bone. The large metatarsal bone is even more strongly constructed than the metacarpal. The shell of compact substance is very thick in the middle of the shaft, especially in front and internally.
The small metatarsal bones are a little longer than the corresponding metacarpals. The external (fourth) metatarsal is relatively massive, especially in its upper part. The head is large and outstanding, and bears two facets above for the fourth tarsal, and two in front and internally for articulation with the large metatarsal; elsewhere it is roughened for attachment. The internal (second) metatarsal is much more slender than the outer one, especially in its upper part. The head bears two facets above for the first and second tarsals, and sometimes one for the third tarsal.
THE PHALANGES AND SESAMOIDS
The axis of the phalanges of the hind limb is about five degrees less oblique than that of the fore limb, and the chief differences in the form and size of the bones are as follows:
The first phalanx is a little shorter, wider above, and narrower below.
The second phalanx is narrower and slightly longer.
The third phalanx is narrower, the angle of inclination of the wall surface is a little (ca. 5 degrees) greater, the sole surface is more concave, and the wings are less prominent and closer together.
The proximal sesamoids are a little smaller, except in thickness. The third sesamoid or navicular bone is narrower and shorter.
SKELETON OF THE OX
VERTEBRAL COLUMN
The vertebral formula is C7T13L6S5Cy18–20.
The cervical vertebræ are much shorter than those of the horse and are smaller in their other dimensions. The articular processes are smaller than in the horse, and a plate of bone connects each two of the same side. The transverse processes of the third, fourth, and fifth are double; the upper part projects backward, and is short and stout; the lower part is directed downward and forward, and is longer and more plate-like. The lower part of the sixth transverse process is a large, thick, quadrilateral and almost sagittal plate, directed downward. The seventh transverse process is single, short, and thick, and presents no foramen transversarium; it is in series with the upper part of the preceding processes. The spinous processes are well developed, and increase in height from before backward. They are directed upward and forward, with the exception of the last, which is nearly vertical and is about four or five inches (ca. 10 to 12 cm.) in height. The summit of that of the third bone is usually bifid. The ventral spines are prominent and thick in their posterior part; they are absent on the last two.
The atlas has a large rough tuberosity on its dorsal arch. The ventral arch is very thick. The wings are less curved than in the horse, and the foramen transversarium (posterior foramen) is absent. The cavities for the occipital condyles are divided into upper and lower parts by a non-articular area, and are separated by a narrow interval below. The posterior articular surfaces are flattened behind and are continued into the vertebral canal, forming an extensive area for the odontoid process of the axis.
The axis is short. The spine projects a little in front, and increases in height and thickness behind; its posterior border descends abruptly. The odontoid process (dens) is wide, and its upper surface is deeply concave from side to side. The intervertebral foramen is circular and not so close to the anterior border of the arch as in the horse. The posterior notches are not so deep. The transverse processes are stouter, but the foramen transversarium is small and sometimes absent.
The thoracic vertebræ, thirteen in number, are larger than those of the horse. The bodies are longer and are distinctly constricted in the middle. They bear a thin-edged ventral crest. The arches—in addition to the usual notches, which are shallow—are perforated in the posterior part by a foramen. The transverse processes are thick and strong, and bear rounded mammillary processes (except at the posterior end of the series); the last two, although prominent, do not always articulate with the ribs. The spinous processes are long. The first is much higher than in the horse, the next two are usually the most prominent, and behind this there is a very gradual diminution in height. The backward slope, slight at first, increases to the tenth; the last is vertical and lumbar in character. The summit is usually pointed on the first, and the thickening on those further back is less than in the horse. The width diminishes from the fifth to the eleventh usually. Both borders of the spines are in general thin and sharp, but the last three or four sometimes have thick posterior margins.
Fig. 88.—Skeleton of Cow.
1.H., Atlas; 7.H., seventh cervical vertebra; 1.R., first thoracic vetrebra; 6.R., sixth rib; 12.R., twelfth thoracic vertebra; 13.R., last rib; 1.L., first, 6.L., last lumbar vertebra; K, sacrum; 1.S., first coccygeal vertebra; 6.K., sixth costal cartilage; x, wing of atlas; 1, scapula; 1′, cartilage of scapula; 2, spine of scapula; 3, acromion; 4, humerus; 4′, external condyle of humerus; 5, external tuberosity of humerus; 6, deltoid tuberosity; 7, ulna; 8, olecranon; 9, radius; 10, carpus; 11, accessory carpal bone; 12, metacarpus; 13, phalanges; 14, sternum; 14′, manubrium; 14″, xiphoid cartilage; 15, ilium; 16, external angle of ilium; 16′, internal angle of ilium; 17, tuber ischii; 18, femur; 19, trochanter major; 20, patella; 21, tibia; 21′, external condyle of tibia; 22, tarsus; 23, distal end of fibula; 24, tuber calcis; 25, metatarsus; 26, phalanges. (After Ellenberger-Baum, Anat. für Künstler.)
The lumbar vertebræ, six in number, are much longer than in the horse. The bodies are much constricted in the middle, expanded at either end, and bear rudimentary ventral crests. The fourth and fifth are usually the longest. The intervertebral foramina are often double in the anterior part of the series, and are very large further back. The articular processes are large, and their facets are more strongly curved than in the horse. The transverse processes all curve forward. They are separated by considerable intervals, and form no articulations with each other or with the sacrum. Their borders are thin and irregular, and often bear projections of variable size and form. The first is the shortest and the length increases to the fifth, the last being considerably shorter. The spinous processes are relatively low and wide, the last being the smallest; their summits are moderately thickened.
The sacrum is longer than that of the horse. It consists originally of five segments, but fusion is more complete and involves the spinous processes, which are united to form a median sacral crest, with a convex thick and rough margin. A lateral crest is formed by the fusion of the articular processes. The pelvic surface is concave in both directions, and is marked by a central groove, which indicates the course of the middle sacral artery. The inferior sacral foramina are large. The wings are quadrangular, short, compressed from before backward, and high dorso-ventrally. They have an extensive anterior surface, which is concave from side to side, and non-articular. The posterior surface is rough, and bears a triangular area below for articulation with the ilium. The body of the first segment is very wide, and the entrance to the sacral canal correspondingly wide and low. The anterior articular processes are large, and are concave and semicylindrical in curvature internally. The lateral borders are thin, sharp, and irregular. The apex is wider than in the horse, and the posterior end of the crest forms a pointed projection over the opening of the sacral canal.
The coccygeal vertebræ are longer and better developed than in the horse. The first five or six have complete arches and spinous processes. The transverse processes are relatively large in the anterior part of the series, in which there are also anterior articular processes (which do not articulate), and a pair of ventral spines which form a hæmal groove for the middle coccygeal artery.
Vertebral curves: The cervical curve is very slight and is concave dorsally. The thoracic and lumbar regions form a gentle curve, concave ventrally. The promontory is more pronounced than in the horse, especially in subjects in which the sacrum is inclined upward behind. Another promontory occurs at the junction of the sacrum and first coccygeal vertebræ.
Length: The following table gives the lengths of the regions of a shorthorn cow of medium size:
| Cervical | 47 cm. |
| Thoracic | 75 cm. |
| Lumbar | 40 cm. |
| Sacral | 24 cm. |
| Coccygeal | 75 cm. |
| 261 cm. |
Variations: Sometimes fourteen thoracic vertebræ and fourteen pairs of ribs are present; reduction to twelve with the normal number of lumbar vertebræ is very rare. According to Franck, there are sometimes seven lumbar vertebræ with the normal number in the thoracic region. The number of coccygeal vertebræ may vary from sixteen to twenty-one.
THE RIBS
Thirteen pairs of ribs are normally present, of which eight are sternal and five asternal. They are in general longer, wider, flatter, less curved, and less regular in form than in the horse. The eighth, ninth, and tenth are the longest and widest. The width of most of the ribs increases considerably in the middle, and the breadth of the intercostal spaces is correspondingly diminished. The neck is long, and forms (except in the posterior part of the series) a smaller angle with the shaft than in the horse. The articular surface of the tubercle is concave transversely, except on the last two or three, where the facet is small and flat or absent. The lower ends of the second to the tenth or eleventh inclusive form diarthrodial joints with the costal cartilages. The first costal cartilages are very short; they articulate by their internal surfaces with the sternum, but not with each other.
The presence of a fourteenth rib is not very rare. It is usually floating and may correspond to an additional thoracic vertebra or to the first lumbar. Reduction of the thirteenth is more common. The eighth cartilage often does not reach the sternum, but articulates with the seventh.
The sternum consists of seven sternebræ, most of which are developed from two lateral centers. It is wider, flatter, and relatively longer than in the horse, and the ventral crest or “keel” is absent. The manubrium is somewhat wedge-shaped and laterally compressed. Its base forms a diarthrodial joint with the body of the bone, and laterally it bears extensive facets for articulation with the first pair of costal cartilages. The body widens from before backward, but behind the last pair of costal facets it becomes much narrower. The ventral surface is prominent on the second and third segments, concave further back. The lateral borders are notched for the passage of vessels. The cariniform cartilage is absent. The xiphoid cartilage is like that of the horse but is smaller.
THE THORAX
The bony thorax is shorter than in the horse. The inlet is higher. The roof is short, and the floor wider and relatively longer. The transverse diameter is wider in the posterior part. The summits of the spinous processes are almost in a straight line from the second thoracic to the middle of the lumbar region.
Bones of the Skull
Bones of the Cranium
The occipital bone is situated in the lower part only of the posterior surface of the skull, and is separated from the highest part (the frontal eminence) by the parietal and interparietal bones. The supraoccipital, interparietals, and parietals fuse before birth or soon after, and the mass so formed is separated from the lateral parts of the occipital bone by a transverse suture in the skull of the calf. Above this suture is a central tuberosity, to which the ligamentum nuchæ is attached, and the surface on either side is depressed and rough for muscular attachment. Below the suture the bone is much wider than that of the horse. The foramen magnum is wide, so that the condyles are further apart except below. The paramastoid processes are short and wide and are bent inward. Two constant foramina are found in the condyloid fossa; the anterior one is the hypoglossal, the other (sometimes double) conducts a vein from the condyloid canal. The latter passes upward from a foramen on the inner side of the condyle and opens into the parieto-temporal canal. The cranial surface of the supraoccipital presents a central depression, and above this is a variable but never very pronounced eminence, which corresponds to the tentorium osseum of the horse. On either side is a groove leading to the parieto-temporal canal. The basilar process is short and wide; its cranial surface is deeply concave, and the internal spheno-occipital crest is prominent. Two large tubercles below mark the junction with the sphenoid. The foramen lacerum is short and very narrow. In the adult animal the bone is excavated to contain an air-cavity which is regarded as a part of the frontal sinus.
The sphenoid bone is short. The cranial surface of the body presents a deep sella turcica, in front of which it rises abruptly. The high anterior part bears a central ridge (Rostrum sphenoidale), which joins the crista galli of the ethmoid. Two foramina occur on either side. Of these, the large anterior one is equivalent to the foramen rotundum, lacerum orbitale, and patheticum of the horse. The posterior one is the foramen ovale, which transmits the inferior maxillary nerve. The orbital wing is thick and is overlapped by the frontal in such manner as to appear externally to divide into two branches; the anterior part joins the ethmoid close to the sphenopalatine foramen, and contains a small sinus which communicates with an ethmoidal meatus. The temporal wing is small, but forms a prominent thick pterygoid crest. The pterygoid process is wide, and the pterygoid or alar foramen is absent. The sphenoidal sinus is absent in the calf and small in the adult; it communicates by one or two small openings with an ethmoidal meatus, and so with the nasal cavity.
Fig. 89.—Skull and Atlas of Ox, Lateral View.
9, Zygomatic arch; 11, coronoid process; 12, supraorbital process; 13″, paramastoid or styloid process; 13‴, occipital condyle; 14, parietal bone; 15, frontal bone; 16, squamous temporal bone; 17, external auditory meatus; 18, temporal condyle; 19, orbital surface of lacrimal bone; 20, malar bone; 21, facial surface of lacrimal bone; 22, nasal bone; 23, nasal process of premaxilla; 24′, incisor teeth; 26, maxilla; 27, facial tuberosity; infraorbital foramen in front of 27; 28′, molar part of ramus of mandible; 30, broad vertical part of ramus; 30′, angle of jaw; 31, condyle of mandible; 32, atlas; x, wing of atlas. (After Ellenberger-Baum, Anat. für Künstler.)
The ethmoid bone has an extensive perpendicular plate. The lateral mass consists of five endoturbinals and eighteen ectoturbinals (Paulli). The largest ethmoturbinal is so extensive as to be termed a third or middle turbinal bone; it projects forward between the upper and lower turbinals. The lamina papyracea appears to a small extent externally in the pterygo-palatine fossa, forming part of the upper margin of the sphenopalatine foramen.
The interparietals are primitively paired, but unite before birth. As already mentioned, fusion occurs before or shortly after birth with the parietals and supraoccipital. No distinct tentorium osseum is present.