Part 28

B. =A. mesenterica superior= (Fig. 126, _d_).--The superior mesenteric artery is larger than the cœliac. It supplies the blood to the small intestines and caudal portion of the pancreas and to the ascending and transverse colon. It arises from the ventral side of the abdominal aorta about one centimeter caudad of the cœliac axis and passes caudoventrad, forming a curve with the convexity dextrad. It gives off the =pancreaticoduodenalis inferior=, =colica media=, =colica dextra=, =ileocolica=, and numerous branches to the small intestine.

1. =A. pancreaticoduodenalis inferior= (Fig. 125, _k_).--This passes to the caudal end of the pancreas and a part of the duodenum, anastomosing with the pancreaticoduodenalis superior.

2. =A. colica media= is a large branch to the transverse and descending portions of the large intestine. It divides and sends branches in both directions which anastomose with the colica dextra and with branches from the inferior mesenteric arteries.

3. =A. colica dextra.=--A small branch which passes to the ascending and transverse colon, anastomosing with the colica media and ileocolica. It is sometimes absent.

4. =A. ileocolica.=--This passes to the cæcum and supplies that structure, sending branches to the ileocolic valve and the caudal end of the ileum, and anastomosing with the colica dextra and the intestinal branches of the superior mesenteric.

5. The superior mesenteric now divides into about sixteen terminal branches which pass to the small intestine. In many cases these branches unite near the intestine, forming arches, and from these arches numerous short branches pass to the intestine.

3. =A. adrenolumbalis= (or =lumboabdominalis=) (Fig. 126, _e_).--This rises from the aorta, one on each side, about two centimeters caudad of the superior mesenteric. Each passes laterad onto the dorsal body wall, supplying the muscles of this region. A large branch passes caudad along the surface of the muscles dorsad of the kidney and anastomoses with the iliolumbar artery. From the adrenolumbalis rises usually:

=A. phrenica= (_f_).--The phrenic artery rises either from the cœliac (_c_) or the adrenolumbalis (_e_) and passes to the diaphragm, near its dorsal border. In the diaphragm it passes ventrad, lying at the medial margin of the costal portion of the diaphragm, as far as its sternal portion, where it unites with the artery of the opposite side. The two thus form an arch, from which radiating arteries pass off to supply the diaphragm.

4. =A. renalis= (_g_).--The two renal arteries arise from the sides of the aorta, usually at about the same point, so that the left passes caudolaterad and the right craniolaterad (owing to the position of the kidneys). The artery usually divides just before entering the kidney (2). It passes dorsad of the vein (_t_). The renal artery sometimes sends a branch to the suprarenal body (1). It also occasionally gives origin to the spermatic artery (_h_).

5. =A. spermatica interna= (_h_).--This rises from the aorta on each side at about the level of the caudal ends of the kidneys, and passes laterad (or it may arise from the renal). In male specimens the artery turns caudad, along with the corresponding vein (_u_), and passes to the inguinal canal. Thence it passes along with the vas deferens and the vein (forming all together the spermatic cord) to the testes and the other structures in the scrotum.

In females (Fig. 112, 2, page 265) the artery is larger and passes more nearly directly laterad, being much convoluted. It passes to the ovary, being now called the =ovarian artery=. It sends branches into the ovary (_c_) and to the cranial end of the uterus (_f_); the latter anastomosing with branches of the uterine artery (3).

6. =A. mesenterica inferior= (Fig. 126, _i_).--The inferior mesenteric artery has its origin from the aorta at about the level of the last lumbar vertebra. It passes toward the large intestine, and near it divides into two branches, the =colica sinistra=, which passes craniad along the descending colon, anastomosing with the colica media, and the =superior hemorrhoidal=, which passes caudad along the descending colon and rectum and anastomoses with the middle hemorrhoidal (page 308).

7. =A. iliolumbalis= (Fig. 126, _j_).--The iliolumbar arteries arise from the aorta about two centimeters caudad of the inferior mesenteric and pass laterad over the ventral surface of the psoas minor and iliopsoas muscles. Each divides into two main branches, one passing caudad and the other craniad; these supply the muscles of this region. The cranial branch anastomoses with branches of the adrenolumbalis (_e_). The caudal branch sends an artery through the abdominal wall to appear at the cranial edge of the thigh; it passes onto the lateral surface of M. sartorius and extends here some distance distad.

8. =A. lumbalis.=--There are usually seven pairs of lumbar arteries, passing almost directly dorsad from the dorsal surface of the aorta; the first pair arising just craniad of the diaphragm, the last at the same level as the origin of the external iliac. The two arteries of a pair usually arise from the aorta one behind the other, or they may arise by a common trunk. They correspond to the intercostal arteries. They pass between the centra of the vertebræ and the muscles of the dorsal region, and send one main branch laterad, the other dorsad; both supply the dorsal muscles. From the dorsal branch small arteries pass into the vertebral canal to join the anterior spinal artery.

9. =A. iliaca externa= (Fig. 126, _k_).--The external iliac artery passes obliquely caudad from the aorta, lying ventrad of the common iliac vein and against the medial surface of the psoas minor muscle. It passes onto the ventral surface of this and the iliopsoas and at the same time reaches the tendon of the abdominal muscles; through a small opening in this tendon lying ventrocaudad of that for the iliopsoas, it leaves the abdominal cavity. On its emergence from the abdominal cavity onto the medial surface of the thigh it receives the name =A. femoralis= (_m_). The branches of the external iliac artery are described below (page 309).

10. =A. hypogastrica= (or iliaca interna) (Fig. 126, _l_).--The hypogastric or internal iliac arteries are given off from the aorta usually within a centimeter caudad of the external iliac. Each passes caudolaterad, lying on the medial side of the common iliac vein, and divides into branches which supply the structures within the pelvis and the muscles about the pelvic wall. There is much variation in the origin and relations of the branches of this artery. The following seems to be a very common arrangement: A very short distance from the origin the =umbilical= artery (_n_) is given off. The hypogastric artery then extends two or three centimeters and gives off =A. glutea superior= (_p_), which passes at once to the pelvic wall. A little farther caudad the hypogastric divides into the =middle hemorrhoidal= (_r_), to the rectum, and the =glutea inferior= (_q_), which passes out of the pelvis.

Branches of the hypogastric artery:

_a._ =A. umbilicalis= (Fig. 126, _n_).--This small artery arises from the hypogastric about one centimeter from the beginning of the latter, and passes ventrad to the bladder. Here it divides into two branches--the =superior vesical= to the sides of the bladder, the =inferior vesical= to the neck of the bladder and the urethra.

_b._ =A. glutea superior= (Fig. 126, _p_).--This passes dorsolaterad from the hypogastric and reaches the pelvic wall against the medial surface of the ilium. Here it divides into two branches. One passes between the iliopsoas muscle and the ventral border of the ilium to the medial surface of the gluteus maximus; it gives branches to the gluteus muscles, the pyriformis, and the rectus femoris. The other branch passes dorsad of the ilium, sending a branch to the medial surface of the gluteus medius, and a small branch which joins the lateral sacral artery and enters thus the sacral canal.

_c._ =A. hemorrhoidalis media= (Fig. 126, _r_).--The middle hemorrhoidal passes ventrad from the hypogastric, onto the lateral surface of the rectum. It passes caudad near the ventral side of the rectum as far as the anus. A short distance from the origin it gives off a branch which passes almost directly ventrad toward the beginning of the urethra. In the male this branch is small, sending twigs to the urethra and the prostate. In the female it is much larger, forming =A. uterina= (Fig. 112, 3, page 265). The uterine artery turns craniad onto the uterus, which it supplies, passing to the cranial end of the uterine cornu and anastomosing with the ovarian artery.

The middle hemorrhoidal gives off in the female branches to the vagina (Fig. 112, _m_) and neck of the bladder (_k_), and a large branch to the urogenital sinus (_n_); it then supplies the anal glands and other structures about the anus, and anastomoses with the terminal branches of the hemorrhoidalis superior. In the male branchlets are given to the urethra, to the bulbourethral (or Cowper’s) gland, and to the penis. The =A. dorsalis penis= is a small branch which passes along the median dorsal groove of the penis to the glans. The middle hemorrhoidal then supplies the structures about the anus and anastomoses with the superior hemorrhoidal, as in the female.

_d._ =A. glutea inferior= (Fig. 126, _q_).--This is the terminal portion of the hypogastric. It passes along with the great sciatic nerve to the great sciatic notch, and reaches the medial surface of M. pyriformis. It divides into branches which supply the gluteus and pyriformis muscles, while a small branch accompanies the great sciatic nerve. A small branch also passes onto the lateral surface of the tail, extending caudad along its side.

11. =A. sacralis media= (Fig. 126, _o_).--This is the continuation of the aorta into the sacral and caudal regions. It extends to near the end of the tail, lying in the ventral middle line against the sacral and caudal vertebræ. In the caudal region it passes through the hæmal arches, covered by the chevron bones. Between the vertebræ it gives off side branches comparable to the intercostal and lumbar arteries of the aorta.

Branches of the sacralis media:

_a._ =A. sacralis lateralis.=--Behind the first sacral vertebra a large branch, the lateral sacral, is given off on each side. This enters the first anterior sacral foramen, gives a branch to the structures in the sacral canal, and sends a dorsal branch out through the posterior sacral foramen to the muscles on the dorsal side of the sacrum.

Similar but smaller branches are given off between the succeeding vertebræ, sacral and caudal.

_The External Iliac and its Branches._--The origin of the external iliac (Fig. 126, _k_) is described above (page 307). It gives off the following branches:

1. =A. profunda femoris= (Fig. 126, _y_).--This is given off just before the external iliac leaves the abdominal cavity. It passes caudad, and about one centimeter from its origin it gives off three branches, sometimes all separately, sometimes two in common. One of these passes mediad in the lateral ligament of the bladder and ramifies on the lateral surface of that organ. A second passes through the abdominal wall and into the fat on the medial surface of the thigh; it sends a branch caudad toward the external genital organs, while its main trunk passes distad in the subcutaneous fat almost to the knee. From one of these two a small branchlet passes in the male to the spermatic cord and accompanies this to the testis; it represents thus the =external spermatic artery=. The third branch, =A. epigastrica inferior=, passes directly to the ventral surface of the rectus abdominis muscle, on which it passes craniad, sending branches to the muscles of the abdominal walls. It anastomoses with terminal branches of the internal mammary artery.

The profunda femoris itself passes between the iliopsoas and the pectineus muscles, then to the medial surface of the adductor femoris. It divides into branches which supply the pectineus, adductor longus, adductor femoris, caudofemoralis, quadratus femoris, semimembranosus, and semitendinosus.

2. =A. femoralis= (Fig. 127).--This is the continuation of the external iliac onto the medial surface of the thigh. The artery lies in a triangular depression between the borders of the sartorius (1) and gracilis (9) muscles. The floor of the depression is formed by the adductor longus (6), pectineus (5), vastus internus, and rectus femoris (3) muscles. This triangular depression is known as the =iliopectineal= fossa, or Scarpa’s triangle; it contains also the femoral vein (_a_) and saphenous nerve (_g_), which pass along with the artery. The artery extends distad, and at about the middle of the length of the thigh it passes, along with the vein and nerve, into a groove between the vastus medialis and the adductor femoris. This groove is converted into a canal by the overlying aponeurosis; it is known as =Hunter’s canal= or the =canalis adductorius=. At the distal end of the adductor femoris the femoral artery ceases to be superficial and passes between the vastus medialis and the semimembranosus to the popliteal space; it now receives the name =A. poplitea=.

Branches of the femoral artery:

_a._ =A. circumflexa femoris lateralis= (Fig. 127, _d_).--The lateral circumflex arises from the femoral about one centimeter from its emergence from the abdominal cavity. It passes craniad and laterad and divides into two main portions. One part passes between the rectus femoris and vastus medialis, gives branches to these muscles, and sends an ascending branch to the structures about the hip-joint, and a descending branch into the vastus medialis muscle. The remainder of the lateral circumflex passes along the inner (lateral) surface of the sartorius (1) to the cranial border of the leg, giving branches to the sartorius (1) and tensor fasciæ latæ (2).

_b._ A large =muscular= branch (_e_) passes caudad (or ventrad) and distad across the distal end of the adductor femoris (7) and between the gracilis (9) and semimembranosus, supplying these muscles. Other small muscular branches may be given off from both sides of the femoral.

_c._ =A. articularis genu suprema= (_h_).--The superior articular artery arises from the femoral, either in common with the saphenous artery or separately, a little proximad of the point where the femoral ceases to be superficial. It passes toward the knee, between the vastus medialis and semimembranosus, and covered by the sartorius (1), and ramifies over the medial surface of the knee-joint and in the structures just proximad of the joint.

_d._ =A. saphena= (_f_).--The saphenous artery frequently takes origin in common with the superior articular (_h_), but may arise separately at about the same level. It passes distad across the gracilis (9), accompanied by the saphenous nerve (_g_) and vein, sends several branches dorsad (toward the knee), and at about the middle of the lower leg it divides into two main branches, a =dorsal= branch (_k_), passing to the dorsum of the foot, and a =plantar= branch (_j_), to the sole of the foot. The dorsal branch is accompanied by the main saphenous nerve (_g_) and vein. It sends one or two branches to the medial side of the ankle-joint, passes then onto the dorsum of the foot, and divides into four main branches. The medial one passes along the medial side of the medial digit; the other three pass to the intervals between the digits. Each divides into two branches which supply the contiguous sides of the two digits between which the interval lies. The dorsal branch thus supplies arteries to the sides of all the digits except to the lateral side of the lateral digit. This is supplied by A. suralis.

The plantar branch (_j_) is larger than the dorsal. It passes distad on the medial surface of the flexor longus hallucis, accompanied by the tibial nerve, and across the space between the tendon of Achilles and the flexor. It gives superficial and deep branches to the structures about the ankle-joint, and sends inward a branch from the lateral side (Fig. 128, _d_) which joins the termination of A. tibialis anterior to form the plantar arch. It then passes distad along the plantar surface of the foot, nearer its medial border. Beneath the pad in the sole of the foot it divides into three branches which supply the interosseous spaces between the three digits.

_e._ =A. poplitea.=--The main trunk of the femoral artery passes between the vastus medialis and the semimembranosus and then through the distal portion of the adductor femoris to reach the popliteal space. This is the space ventrad (or caudad) of the knee, between the biceps femoris on one side and the semimembranosus on the other. Here the artery receives the name =A. poplitea=, or popliteal artery. The popliteal artery gives off a number of large branches as it passes through the popliteal space, passes between the condyles of the femur and underneath the popliteal muscle, and finally turns dorsolaterad between the tibia and fibula, just distad of the head of the fibula. It now receives the name =A. tibialis anterior= and passes distad along the dorsal (anterior) border of the fibula.

Branches of the popliteal artery:

1. =A. suralis.=--This is a large branch which passes distad from the caudal side of the popliteal artery. It sends branches to the biceps and to the fat in the popliteal space, and passes onto the ventral border of the lateral head of the gastrocnemius. It sends branches to both heads of the gastrocnemius and to the popliteus, passes distad onto the lateral surface of the tendon of Achilles, and may be traced to the proximal portion of the dorsolateral side of the foot, where it sends many branches to the integument about the ankle-joint. It then passes along the lateral side of the foot and supplies the artery on the lateral side of the fifth digit.

2. =Aa. genu posteriores.=--Several small arteries which pass to the knee-joint.

3. =Rami musculares.=--Numerous small branches to the muscles about the popliteal space.

4. =A. tibialis posterior.=--This is the largest branch of the popliteal artery, which it leaves just before the latter passes beneath the popliteal muscle. The tibialis posterior passes at first mediad, then turns distad, passes across the popliteus muscle onto the surface of the flexor longus hallucis, and ramifies in the substance of this muscle and its tendon. It gives branches also to the gastrocnemius and soleus. (It does not pass into the foot as does the corresponding artery in man.)

5. =A. tibialis anterior.=--The anterior tibial artery is the continuation of the popliteal after its passage through the interosseous membrane between tibia and fibula to the dorsal side of the lower leg. Here it passes distad, lying against the interosseous membrane, between the extensor longus digitorum and the tibialis anterior muscle, or partly imbedded in the substance of the latter. It passes, lying beneath the tendons of these muscles, through the transverse ligament proximad of the malleoli, thus reaching the dorsum of the foot. It extends distad across the tarsus to the space between the second and third metatarsals, and through this space to the plantar side of the foot (Fig. 128). Here it receives one or two small branches (_a_ and _d_) from the plantar branch of A. saphena (forming with them the =plantar arch= (_c_)), and passing distad and slightly laterad, divides into three main portions (_e_). These (=Aa. digitales plantares=) pass to the three intervals between the digits. The medial one passes along the lateral side of the second digit; the next divides, sending a branch to the lateral side of the third digit and the medial side of the fourth; the lateral one passes along the medial border of the fifth digit. The Aa. digitales plantares send numerous branches to the interosseous muscles.

Branches of the tibialis anterior:

_a._ =A. tibialis recurrens.=--Immediately after passing through the interosseous membrane the anterior tibial sends a small artery proximad to the knee-joint.

_b._ =Rami musculares.=--Numerous short branches throughout the course of the artery, to the muscles about it.

_c._ =Ramus superficialis.=--A larger branch leaves the lateral surface of the artery about one-third the distance from the knee to the ankle and passes along with the superficial peroneal nerve, at first beneath M. peroneus longus, then superficially. It passes onto the dorsal surface of the foot and becomes connected with terminal branches of =A. saphena=.

_d._ =A. tarsea medialis.=--This arises from the tibialis anterior just distad of the transverse ligament through which it passes at the ankle, passes over the medial surface of the astragalus, and is distributed to the ligaments about the ankle-joint. It anastomoses with the plantar branch of A. saphena.

_e._ =A. metatarsea.=--The metatarsal artery passes laterad from the tibialis anterior at the distal boundary of the tarsus, on the dorsal surface of the foot. It sends branches distad in the intervals between the third and fourth and the fourth and fifth metatarsals.

The distal branches (Fig. 128) of the tibialis anterior have been described in the general description of the artery.

THE VEINS. VENÆ.

=Venæ pulmonales. The Pulmonary Veins.=

The pulmonary veins follow in the lungs the course of the bronchi. They enter the left auricle in three groups (Fig. 116, page 276). The first of these (_i_) comes from the anterior and middle lobes of the right side, the second (_h_) from the corresponding lobes of the left side, and the third (_g_) from the terminal lobes of both sides. Each group is composed of two or three veins and opens into a sinus or extension of the auricle. The sinuses are from their position dextral (_i_), sinistral (_h_), and dorsal (_g_).

=The Veins of the Body.=