4. The subclavian artery (Arteria subclavia), (Fig. 150 s). The subclavian artery arises from the systemic arch immediately behind the occipito-vertebral artery at the level of the second or third vertebra. The artery then runs outwards alongside and in front of the brachial nerve, between the M. subscapularis and the M. triceps to the arm, where it is known as the brachial artery; in its course it gives off:‍—

a. The Arteria costo-cervicalis (Fig. 150, 1). This artery arises near the systemic arch, and runs backwards, parallel to the vertebral column, over the brachial nerve, and across the transverse processes of the vertebrae. It is distributed more especially to the M. obliquus internus.

b. The Arteria coraco-clavicularis (Fig. 150, 2) arises more externally than the last artery; it accompanies the coraco-clavicular nerve on the dorsal surface of the ventral portion of the shoulder-girdle, and passes between the M. deltoideus and M. subscapularis into the Foramen ovale, where it divides to supply these muscles and the M. pectoralis.

c. The Art. scapularis posterior (Fig. 150, 3), a small branch arising opposite at the tip of the second transverse process and passing backwards over the MM. transverso-scapulares, to which it is distributed.

d. The Art. scapularis superior (Fig. 150, 4) accompanies several nerves between the M. subscapularis, M. transverso-scapularis major, and the long head of the M. triceps towards the dorsal surface, where it is distributed to the MM. infraspinatus, latissimus dorsi, etc.

e. The Ramus cutaneus maxillaris.

f. The Art. subscapularis (Fig. 150, 6) is distributed in the subscapular muscle.

A. The brachial artery (Arteria brachialis), (Fig. 150) accompanies the brachial nerve under cover of the long head of the M. triceps and over its inner head to the Plica cubiti, into which it sinks near the tendon of the M. sternoradialis; beyond this point it is continued as the ulnar artery. In its course the brachial artery gives off:‍—

a. The Arteria pectoralis (Fig. 150 p).

b. The Arteria cutanea medialis superior (Fig. 150 c).

c. The radial artery (Arteria radialis), (Fig. 150 R) which winds round the humerus with the radial nerve between the muscles of the outer side of the forearm, to which it gives branches: in the palm of the hand it passes between the M. extensor carpi ulnaris and the M. flexor antibrachii to the dorsal surface of the hand, where it anastomoses with the ulnar artery. In its course it supplies:‍—

(1) Muscular branches to the surrounding muscles.

(2) The Ram. cut. radialis inferior, which arises from the radial artery towards the distal end of the forearm, and passes underneath the M. flexor carpi ulnaris to the skin.

B. The ulnar artery (Arteria ulnaris), (Figs. 150 U, 151 B) accompanies the ulnar nerve towards the hand, passes between the M. flexor digitorum communis and the M. anconeus to the palm of the hand, and then winds round the outer side to the dorsal surface of the carpus to form its terminal branches. The branches are:‍—

(1) The Ram. cutan. med. inferior (Fig. 151 ci); it arises near the wrist-joint and supplies (α) twigs to the skin of the inner surface; (β) a branch downwards, which courses along the inner side of the second finger to its tip; and (γ) a branch which passes upwards to anastomose with the R. cutaneus medialis superior.

(2) In the palm of the hand a branch (Fig. 151 d) is given off, which divides to form Arteriae digitales volares: one for the second finger, two for the third finger, two for the fourth finger, and one for the fifth finger.

(3) Given off on the dorsum of the hand (Fig. 152) it supplies branches corresponding exactly with those of the palmar surface.

5. The dorsal aorta (Aorta communis s. abdominalis) (Fig. 153 A). The two systemic arches unite at about the level of the sixth vertebra to form the dorsal aorta: as already mentioned the union is very incomplete, the dorsal aorta being practically a continuation of the right systemic arch, and only communicating with the left by means of a small opening. The branches are as follows:‍—

a. The coeliaco-mesenteric artery (Arteria intestinalis communis), (Fig. 153), the true continuation of the left systemic arch, at once divides to form the gastric and mesenteric arteries.

(1) The gastric artery (Arteria gastrica s. coeliaca) (c) immediately divides into two branches:‍—

α. The Ramus dexter s. anterior; this artery gives off the Arteria hepatica to the liver and gall-bladder and passes to the right (anterior) surface of the stomach, running along the attachment of the mesentery and supplying branches forwards to the oesophagus and backwards towards the intestine.

β. The Ramus sinister s. posterior passes to the left (posterior) surface and behaves like the Ram. dexter.

(2) The mesenteric artery (Arteria mesenterica superior and inferior, and the Arteria splenica), (Fig. 153 m) supplies:‍—

α. The superior mesenteric artery, which supplies the upper part of the intestine, and gives off a recurrent branch to the stomach, which anastomoses with the gastric arteries.

β. The splenic artery to the spleen.

γ. The inferior mesenteric artery to the lower part of the intestine.

All the arteries to the intestine course in lymph-spaces.

b. The urinogenital arteries (Arteriae urino-genitales), (Fig. 154 ug) are four to six small arteries arising from the ventral surface of the aorta between the kidneys: they immediately divide into right and left branches to supply the kidneys, fat-bodies, reproductive organs, and their ducts (see kidney).

c. The lumbar arteries (Arteriae lumbales), are small paired vessels to the neighbouring muscles, and send branches through the intervertebral foramina to the vertebral canal. Sometimes these arteries arise from the Art. spinalis or Art. vertebralis, etc.; in the former case they pass outwards from the vertebral canal to the surrounding structures.

d. The haemorrhoidal artery (Art. mesenterica inf. s Art. haemorrhoidalis superior) is a small median artery running from the posterior end of the aorta to the large intestine.

6. Bifurcation of the aorta. The iliac arteries (Arteriae iliacae communes). Opposite the middle of the urostyle the aorta bifurcates to form the iliac arteries; each of these courses on the corresponding sciatic plexus to the thigh, beyond which it is continued as the sciatic artery. The branches of the iliac artery are:‍—

a. The vesico-epigastric artery (Arteria epigastrico-vesicalis), (Fig. 155 ev); it arises near the bifurcation, passes outwards on the plexus, and divides into two branches:‍—

(1) The epigastric artery (Arteria epigastrica) (e) immediately gives off a recurrent branch to the iliac bone and the M. ilio-coccygeus; it then continues to the ventral muscles of the abdominal wall, where it runs forwards on the deeper surface of the M. obliquus internus, and is distributed more especially to this muscle.

(2) The hypogastric artery (Arteria vesicalis) (v) winds downwards around the sciatic plexus to reach the mesentery, along which it courses to the bladder, where it forms a rich anastomosis.

b. The femoral artery (Arteria femoralis s. cruralis), (Fig. 155 f) is the representative of the femoral artery of man, although it does not perform the same functions. The artery passes under the hinder free border of the M. obliquus internus to the thigh, where it lies upon the M. ilio-psoas, and sends twigs to the neighbouring muscles, the skin, and lymph-sac (Lamina inguinalis), and then divides into:‍—

(1) A twig, which runs forwards on the ventral surface of the iliac bone and is covered by the epigastric artery.

(2) A twig, running forwards and downwards on the MM. ilio-psoas, vastus internus, and sartorius, to send branches to the hip-joint.

c. The spermatic artery (Arteria spermatica), which arises, in males, from the iliac artery, and ascends to the Vesicula seminalis.

7. Arteries of the hinder extremity.

A. The sciatic artery (Arteria ischiadica), (Fig. 156 i) is the continuation of the iliac artery; it leaves the pelvis between the hinder (outer) border of the M. coccygeo-iliacus and the inner surface of the origin of the M. ilio-psoas, then lies between the former muscle and the origin of the M. vastus externus. It appears on the thigh between the M. vastus externus (in front) and the M. pyriformis (behind); it is the main arterial trunk for the hinder extremity. The artery courses backwards, lying upon the sciatic nerve and between the M. biceps and the M. semimembranosus; in this course it runs in a lymph-space placed in the Septum femorale superius (see page 259). Arrived at the popliteal space the artery bifurcates to form the peroneal and tibial arteries; near the pelvis it gives off two branches (a) and (b), and in its course along the thigh two branches (c) and (d).

a. The Art. haemorrhoidalis inferior (h) runs backwards and inwards under the M. pyriformis to be distributed in the M. sphincter ani and the skin of the anus.

b. The Art. cutanea femoris posterior v. superior (cf′) runs with the corresponding nerve and the M. pyriformis, and over the M. semimembranosus to the skin of the inner and hinder surfaces of the thigh.

c. The Rami musculares supply the M. semimembranosus, the M. biceps, and the MM. extensores auris; the branch to the M. rectus inferior major pierces the muscle in company with the nerve, and is continued as:‍—

d. The Art. cutanea femoris media (cf″) to the skin of the middle of the inner surface of the thigh. Several small twigs pierce the M. rectus internus minor, reach the skin, and communicate with this artery.

B. The peroneal artery (Art. peronea), (Fig. 156 p) runs outwards under cover of the tendon of the M. biceps femoris, and accompanies the peroneal nerve downwards to give off:‍—

a. The Art. circumflexa genu lateralis superior, which runs forwards on the outer side of the knee, gives a twig to the joint, and is continued as:‍—

b. The Art. cutanea genu lateralis superior (cgl) to the skin of the anterior and outer sides of the knee. It anastomoses with branches of the Arteriae circumflexae genu mediales to form a rich anastomosis (Rete articulare genu): other branches pass upwards to inosculate with the Art. cutanea femoris anterior (cf), and others downwards to anastomose with the next artery.

c. The Art. circumflexa genu lateralis inferior (cgl′) runs under the tendon of origin of the gastrocnemius to the outer side of the knee, and terminates in the skin as the Art. cutanea genu lateralis inferior. Some of the cutaneous twigs pass upwards to anastomose with the Art. cut. genu lat. superior, others downwards to anastomose with the AA. malleolares.

d. A muscular branch (p′) for the M. peroneus; it is the real continuation of the peroneal artery, and runs behind the outer tendon of origin of the gastrocnemius to be distributed in the M. peroneus.

C. The tibial artery (Arteria tibialis), (Fig. 156 t), arises at the bifurcation of the sciatic, and runs inwards, meeting the tibial nerve between the tendons of origin of the M. gastrocnemius, and deep in the popliteal space under cover of the calf-muscles. It then pierces the M. tibialis posticus, and leaves this to perforate the tibio-fibula (see p. 50), appearing again on the anterior surface as the anterior tibial artery. Before meeting the tibial nerve this artery gives off the following branches:‍—

a. The Art. circumflexa genu superior medialis (cgm), which winds round to the front of the knee-joint, and gives off a cutaneous branch, the Art. cutanea genu medialis superior, which is distributed in the skin of the inner side of the knee and anastomoses above with the Art. cutanea femoris media, below with the following branches (b, c, and d).

b. The Art. circumflexa genu inferior medialis (cgm′) supplies twigs to the knee-joint, and passes to the skin of the knee and inner surface of the calf as the Art. cutanea inferior medialis.

c. Muscular twigs to the M. gastrocnemius.

d. The Art. suralis (su); this accompanies the N. suralis downwards along the calf-muscle, and is distributed in the skin of the inner side of the heel.

e. While passing between the fibres of the M. tibialis posticus, the tibial artery gives off muscular twigs; one larger than the rest is known as the Ramus descendens.

D. The anterior tibial artery (Arteria tibialis antica), (Fig. 157 t.a.) is the continuation of the tibial artery after piercing the tibio-fibula. It runs downwards on the anterior surface of the leg, then between the two heads of the M. tibialis anticus to the dorsum of the foot, where it is continued as the Arteria dorsalis pedis. It supplies:‍—

a. Rami musculares to the M. peroneus, M. extensor cruris, and to the M. flexor tarsi anterior.

b. The Art. cutanea cruris inferior (c.c.i.) passes between the two heads of the M. tibialis anticus to the skin of the anterior and outer sides of the leg.

c. The Art. cutanea calcanei (c.c.) is given off at the ankle-joint; it runs outwards on the lower end of the tibio-fibula, giving branches to the joint, then backwards between the tibio-fibula and the M. peroneus to be distributed to the skin of the heel. Above it anastomoses with the A. circumflexa genu inf. lateralis, and below with the malleolar arteries.

d. The Art. malleolaris lateralis (ml) arises a little beyond the last artery; it runs outwards under the origin of the M. flexor tarsi, gives branches to the joint and muscles, and terminates in the skin of the outer border and dorsal surface of the foot.

e. The Art. malleolaris medialis (m.m.) arises at about the same level as the Art. malleolaris lat. from the inner border of the anterior tibial artery. It supplies branches to the joint, gives numerous branches to the skin, which anastomose with the Art. suralis, and passes to the inner border of the foot, where it ends by distributing branches to the M. plantaris, the extensor aponeurosis, and, as the Art. cutanea plantaris, to the skin of the sole of the foot.

E. The dorsal artery of the foot (Art. dorsalis pedis), (Fig. 157 t.a.) runs under the M. flexor tarsi posterior to the point ta*, where it is superficial; the artery then bifurcates; the branches are:‍—

a. The Art. tarsea (tr) which arises from the dorsal artery of the foot while under cover of the M. flexor tarsi posterior; it passes to the M. extensor digiti V and to the skin of the dorsum and outer border of the foot. One branch courses along the outer border of the fifth toe to its tip; another passes upwards to anastomose with the neighbouring vessels.

b. The inner branch, formed by the bifurcation of the dorsal artery of the foot, at once divides to form:‍—

(1) The Art. cutanea hallucis (h) to the supplemental great toe.

(2) The Art. interossea dorsalis I (i¹), which at once bifurcates to form two Rami digitales for the first and second toes; these inosculate with the Art. cutanea plantaris, and send twigs to the skin of the inner border of the foot.

c. The outer branch formed by the bifurcation of the dorsal artery divides to form the Arteriae interossei dorsales II, III, and IV (i², i³, i⁴); they are distributed in a rich anastomosis to the web.

d. The Arteria interossea (Fig. 158 i) arises from the dorsal artery of the foot at the tarsus, and perforates the membrane between the astragalus and calcaneum to reach the sole of the foot. It forms a rich subcutaneous plexus on the calcar, and anastomoses with the Rami perforantes (Fig. 158 pf), which pass above the upper borders of the Musculi interossei to reach the plantar surface, where they give off small Rami interossei volares to anastomose with the AA. interosseae dorsales.

III. THE VEINS.

(The arrangement of this section has been modified.)

The blood, distributed to the body by means of the arteries, is returned to the heart by the veins, which conduct the blood directly or indirectly to the auricles. The pulmonary vein opens directly into the left ventricle, the three Venae cavae open into the Sinus venosus.

A. Vein opening into the left auricle.

The pulmonary vein (Vena pulmonalis communis), (Fig. 159 vp). The blood returning from each lung is gathered into a vessel lying along the inner side of the root of the lung. That of the right side is somewhat longer than the left; the two vessels (Venae pulmonales dextra et sinistra) run above the corresponding anterior caval veins to form a common trunk, the pulmonary vein, which opens into the left auricle (see p. 215).

B. Veins opening into the Sinus venosus.

The veins opening into the Si­nus ve­no­sus are the three caval veins; of these the two an­ter­ior open into the an­ter­ior angles of the Si­nus ve­no­sus, the pos­ter­ior into the pos­ter­ior angle.

1. The Anterior Caval Veins (Vena cava superior), (Figs. 133 V, 159 C a) are a pair of large veins opening into the Si­nus ve­no­sus and re­turn­ing to it blood from the fore-limbs and sides of the head. Each vein is formed by the union of a small vein, the ex­ter­nal ju­gu­lar, with two large veins, the in­nom­in­ate and the sub­cla­vian veins.

a. The external jugular vein (Vena ju­gu­la­ris externa), (Fig. 159 je) is formed, at the outer bor­der of the hyoid bone, by the union of two veins:‍—

(1) The lingual vein (Vena lingualis) (Fig. 161 l). This orig­in­ates at the tip of the tongue and passes in a very tor­tu­ous course along the ven­tral sur­face of the hyoid; it receives nu­mer­ous branches from the tongue and hyoid muscles.

(2) The mandibular vein (Vena maxillaris inferior), (Fig. 161 m) runs along the in­ser­tion of the M. sub­max­il­lar­is, and turns in­wards at its hinder bor­der to join the lin­gual vein.

b. The innominate vein (Vena anonyma), (Fig. 160 A) is formed by the union of the in­ter­nal ju­gu­lar and the sub­sca­pu­lar veins. By tracing the in­nom­in­ate vein upwards between the sus­pen­sor­ium and the shoulder-girdle, the in­ter­nal ju­gu­lar vein will be seen to receive the ver­te­bral vein at the outer border of the M. le­va­tor sca­pu­lae. The left in­nom­in­ate vein receives the Vena bulbi an­ter­ior from the Truncus arteriosus (p. 222).

(1) The internal jugular vein (Vena jugularis), (Fig. 160 J) can be traced from the border of the M. levator scapulae upwards and forwards to the hinder part of the prootic bone: it then passes forwards under the lateral process of the prootic, in a groove on the anterior surface of the same bone, towards the hinder angle of the orbit, where it receives the veins from the cranial cavity (see vessels of brain, p. 165), and also a branch from the orbit.

α. [The Vena orbitalis media (Virchow); it arises from the anterior internal angle of the orbit, from the Harderian gland, the nasal cavity, or from other veins on the anterior wall of the orbit. The vessel lies close to the cranium, immediately underneath the Arteria nasalis, and sinks under the M. rectus superior to join the internal jugular vein. In its course it receives the Vena bulbi superior (see eye), and near its termination communicates with the Vena orbitalis posterior.]

β. The Vena vertebralis (Fig. 160 V) arises posteriorly and runs forwards over the transverse processes of the vertebrae, the Musculi intertransversarii, and the M. levat. scapulae, to join the internal jugular vein. In its course it receives branches (Venae spinales) from the vertebral canal through the intervertebral foramina, and cutaneous branches which accompany the corresponding arteries and nerves through the dorsal lymphatic sac. The vein pulsates in consequence of its connection with the anterior lymph-heart (Müller).

(2) The subscapular vein (Vena subscapularis), (Fig. 160 S). This vein arises in the transverse abdominal muscles and the muscles of the shoulder girdle; it unites with the internal jugular vein under the shoulder-girdle.

c. The subclavian vein (Vena subclavia), (Fig. 159) passes backwards from the anterior caval vein on the dorsal surface of the coracoid bone and the clavicle, and then under cover of the Portio sternalis of the M. pectoralis major, to the internal border of the Portio abdominalis of the M. pectoralis major, where it is formed by the union of the cutaneous vein and the brachial vein.

(1) The cutaneous vein (Vena cutanea magna, Ecker; Vena musculo-cutanea, Gruby), (Figs. 160, 161, and 162 c.m.). This vein arises by small branches in the head; these are:‍—

α. The Vena nasalis (Virchow); it arises by an upper and a lower branch from around the nostril, and courses backwards along the superior maxillary bone to about the middle of the orbit, where it joins the facial vein.

β. The Vena orbitalis anterior (Virchow), (Vena ophthalmica anterior, Ecker), (Fig. 160 o) commences at the Harderian gland from a rich anastomosis, receives branches from the floor and anterior wall of the orbit, and joins the facial vein with the Vena nasalis.

γ. The Vena orbitalis posterior (Virchow), (Vena ophthalmica posterior, Ecker), (Fig. 160 o′) arises on the posterior wall of the orbit on the M. pterygoideus; it passes under the Processus zygomaticus to join the facial vein, and in its course receives the Vena ophthalmica (see eye), and communicates with the Vena orbitalis medialis and the internal jugular vein.

δ. The Vena facialis (Fig. 160) is formed about the middle of the orbit by the union of the Vena nasalis and the Vena orbitalis anterior; it courses backwards towards the angle of the jaw. On reaching the M. depressor maxillae, about 4 mm. in front of the angle of the jaw, it passes on to the skin. It receives in its course the Venae palpebrales (Fig. 162) and the Vena orbitalis posterior.

The musculo-cutaneous vein is the direct continuation of the Vena facialis after this has left the upper jaw; it immediately receives one or more twigs (Venae tympanicae), (Fig. 162) from the tympanic membrane and the tympanic cavity.

The vein then courses backwards in the outer wall of the lateral lymph-sac as far as the middle of the trunk, where it passes, by means of the Septum abdominale, to the outer border of the Portio abdominalis of the M. pectoralis; here the vein curves round to pass forwards between the fibres of this muscle to its inner border where it terminates by joining the brachial vein. In the whole of this lengthy course the vein receives numerous branches from the neighbouring parts.

(2) The brachial vein (Vena brachialis) is formed in the Plica cubiti by the union of two veins.

α. The radial vein (Vena radialis) arises on the dorsum of the hand from a venous arch, the distal convexity of which receives the Venae digitales dorsales: the vein courses superficially along the outer side of the forearm to the elbow.

β. The ulnar vein (Vena ulnaris) arises from the veins in the palm of the hand, and courses towards the elbow, lying deeply between the muscles of the inner and outer surfaces of the forearm. In the elbow the vein becomes superficial near the tendon of the M. sterno-cleidoradialis, and joins the radial vein to form the brachial vein.

The cutaneous veins of the fore-limb follow courses corresponding with those of the arteries.

2. The Posterior Caval Vein (Vena cava inferior), (Fig. 159 Cp, 163 v.c.i.). The posterior caval vein is a median vein which, commencing between the kidneys, runs forwards to open into the posterior end of the Sinus venosus. It receives the hepatic, renal, and ovarian or spermatic veins.