578 BLOOD-VASCULAR SYSTEM OF THE HORSE 



the ilium along the ventral border of the iliac head of the obturator internus, ac- 

 companied by the satellite vein and nerve, which lie in front of the artery 

 (Fig. 451J. On reaching the anterior border of the obturator foramen it dips 

 under the obturator internus and passes obliquely through the foramen. In this 

 part of its course it gives off a vesical branch and twigs to the obturator 

 internus and the hip-joint. After its emergence from the pelvic cavity it runs 

 backward on the ventral face of the ischium, passes through the semimembranosus 

 and, in the male, enters the crus penis, forming the arteria profunda penis. It 

 anastomoses with the internal pudic, and usually with the external pudic by a 

 branch which runs forward on the dorsum penis. Large collateral branches are 

 detached to the adductors of the thigh, the biceps femoris and semitendinosus, 

 forming anastomoses with the deep femoral and postei'ior femoral arteries. In 

 the female the terminal part is small and enters the root of the clitoris. 



ARTERIES OF THE PELVIC LIMB 



The main arterial trunk of each pelvic limb descends as far as the lower border 

 of the popliteus muscle, where it divides into the anterior and posterior tibial 

 arteries. . The different parts of the trunk receive special names which correspond 

 to the several regions through which it passes. In the abdomen it is termed the 

 external iliac artery, in the proximal two-thirds of the thigh it is called the femoral 

 artery, while below this it is termed the popliteal artery. 



The External Iliac Artery iFigs. 450, 45 n 

 The external iliac artery (A. iliaca externa) arises from the aorta under the 

 fifth lumbar vertebra, usually just in front of the origin of the internal iliac. It 

 descends at the side of the pelvic inlet along the tendon of the psoas minor, crosses 

 the insertion of that muscle, and reaches the level of the anterior border of 

 the pubis, where it becomes the femoral artery. It is covered by the perito- 

 neum and fascia, and is related behind to the corresponding vein. Its branches 

 are as follows: 



1. The circumflex iliac artery (A. circumflexa ilium profunda) arises from the 

 external iliac at its origin or from the aorta directly. It passes across the iliac 

 fascia toward the external angle of the ilium, near which it divides into two branches. 

 The artery lies between the fascia and the peritoneum and is accompanied by two 

 veins and the external cutaneous nerve of the thigh. The anterior branch gives 

 twigs to the iliacus and psoas muscles, and passes downward and forward in the 

 flank between the obliquus internus and transversus abdominis, in which it ramifies. 

 The posterior branch perforates the abdominal wall and runs downward on the 

 inner face of the tensor fascife latse to the fold of the flank, sui:)])l3'ing branches to 

 that muscle, the panniculus, the pre(Tural lymph-glands, and the skin. 



2. The cremasteric artery (A. spermatica externa) is a very small vessel 

 which arises in a variable manner. It springs most often from the external iliac 

 near its origin, but may come from the circumflex iliac, the aorta between the 

 external and internal iliac, or the latter vessel. It accompanies the cremaster 

 muscle to the inguinal canal, supplies twigs to that mus('l(\ th(> tunica vaginalis, and 

 other constituents of the s])ermatic cord (Fig. 450). 



2a. The middle uterine artery (A. uterina media) of the female is regarded 

 as the homologue of the pnu-eding vessel. It has a similar origin, but is a much 

 larger artery, which passes between the layers of the broad ligament and reaches 

 the horn of the uterus close to its junction Avith the body. It is distributed to 

 both, and anastomoses with the anterior and posterior uterine arteries. 



