754 CIRCULATORY SYSTEM OF THE DOG 
tarsal arteries. From these anastomoses four plantar digital arteries result; of 
these, the central two have a common digital trunk. 
The popliteal and posterior femoral arteries present nothing of special interest. 
The posterior tibial artery is very small, being replaced largely by the saph- 
enous. It supplies twigs to the flexor muscles at the proximal part of the leg. 
The anterior tibial artery descends on the anterior face of the tibia and tarsus 
and is continued as the perforating metatarsal artery, which passes through the 
upper part of the space between the second and third metatarsal bones and concurs 
with the plantar arteries in the formation of the proximal plantar arch. Besides 
muscular and articular branches, the anterior tibial supplies the fifth dorsal meta- 
tarsal artery for the lateral side of the fifth digit. At the proximal part of the meta- 
tarsus it gives off three deep dorsal metatarsal arteries which descend in the in- 
tervals between the metatarsal bones and concur with the superficial dorsal meta- 
tarsal and the plantar arteries in the formation of the digital arteries. The latter 
resemble in general arrangement the corresponding arteries of the thoracic limb. 
The internal iliac artery (Fig. 620) runs backward and a little outward across 
the ilio-psoas, and on reaching the illum divides into parietal and visceral branches; 
it gives off the seventh lumbar artery. The parietal branch is the larger. It runs 
backward on the lateral wall of the pelvis, passes out through the lesser sciatic 
notch, and breaks up into branches which supply the muscles of this region; this 
terminal part may be regarded as the posterior gluteal artery. It gives off the 
following branches: (1) The ilio-lumbar artery passes outward between the ilio- 
psoas and the shaft of the ium and ramifies in the gluteus medius, giving branches 
to the ilio-psoas and tensor fascie late; it may arise from the internal iliac. (2) 
The anterior gluteal artery passes out through the greater sciatic foramen and sup- 
plies branches to the glutei. (3) Muscular branches go to the obturator internus, 
coceygeus, and retractor ani. (4) The superficial lateral coccygeal artery (A. cau- 
dalis lateralis superficialis) passes back at first on the lateral face of the coecygeus and 
continues beneath the skin along the side of the tail. The visceral branch is equiva- 
lent to the internal pudic artery; it passes back below the parietal branch on the 
lateral face of the rectum, retractor ani, and coceygeus. Its chief collateral branches 
are: (1) The umbilical artery, which pursues a flexuous course and supplies twigs to 
the bladder, ureter, and ductus deferens. In the bitch it gives off a large uterine 
artery which ramifies chiefly in the body and neck of the uterus and the vagina 
and anastomoses with the utero-ovarian. (2) The middle hemorrhoidal artery 
arises near the ischial arch, passes upward and forward on the lateral surface of the 
rectum, gains its dorsal surface, and anastomoses with the posterior mesenteric; it 
supplies the rectum and the anus, together with its muscles and glands. (3) A 
small perineal artery is detached to the permeum. In the male the trunk turns 
around the ischial arch as the artery of the penis (A. penis). This vessel, after 
giving off the deep artery of the penis (A. profunda penis), which supplies the 
artery of the bulb (A. bulbi urethra) and enters the corpus cavernosum, is con- 
tinued as the dorsal artery of the penis (A. dorsalis penis) along the dorsum penis. 
In the female the terminal branches of the trunk go to the vulva, vestibular bulb, 
and clitoris. 
THE VEINS! 
The arrangement of the veins is, of course, correlated in general with the 
arterial system, but a few special features are worthy of mention. 
The coronary sinus is a large but short trunk formed by the confluence of the 
cardiac veins; it opens into the right atrium below the posterior vena cava. The 
1 Many of the veins are shown in the illustrations of the arteries. 
