THORAX AND ABDOMEN OF THE HORSE 149 



The corresponding arteries of the female (aa. ovarica^) are shorter 

 and much larger, run between the two layers of the broad ligament, and 

 divide into two branches. The tortuous ramus ovaricus terminates in 

 the ovary. The ramus uterinus becomes the cranial uterine artery, 

 inasmuch as it ramifies along the concave border of the uterine cornu. 



Aa. lumbales. — The lumbar arteries arise in pairs from the dorsal 

 side of the aorta. In all there are six pairs, but the last arises from 

 either the hypogastric or the lateral sacral artery and not directly from 

 the aorta. Each artery disappears almost at once under the psoas 

 muscles and therefore cannot be followed at present. Later it will be 

 seen that the first lumbar artery passes between the transverse processes 

 of the first and second lumbar vertebnt : the sixth passes between the 

 sixth lumbar and the first sacral vertebrae. 



A. ILIACA EXTERNA. — The external iliac artery leaves the abdominal 

 aorta at the fifth lumbar vertebra. From its origin it pursues a curved 

 course, close to the brim of the pelvis, under peritoneum and fascia, to 

 the pecten of the pubis, where it enters the thigh as the femoral artery. 

 Lateral and somewhat cranial to the artery are the psoas minor and 

 ilio-psoas muscles ; while lateral and caudal to it are the common iliac 

 and external iliac veins. 



The following are the branches of the external iliac artery : — 



(1) A. circumjiexa ilium profunda. — It is well to remember that, 

 on one or both sides of the body, the deep circumfiex iliac artery may 

 arise directly from the aorta. Generally, however, it leaves the external 

 iliac close to the origin of this vessel from the aorta. Whatever its 

 source, the deep circumflex artery runs in a lateral direction at right angles 

 to the long axis of the body between the peritoneum and the psoas 

 minor and major muscles, accompanied by a vein on each side. At the 

 lateral border of the psoas major it divides into two branches. 

 The cranial branch has already been encountered between the internal 

 oblique and transverse muscles of the abdominal wall. The caudal 

 branch pierces the oblique abdominal muscles to appear underneath the 

 m. tensor fasciae lata; close to the coxal tuber of the ilium. Its sub- 

 sequent course beneath this muscle is examined during the dissection 

 of the pelvic limb. 



(2) A. spermatica externa. — The external spermatic artery is a 

 small vessel with a very variable origin. It may arise from the deep 

 circumflex iliac artery or even from the hypogastric, instead of from the 

 external iliac. In the male it follows the caudal border of the cremaster 

 muscle down the inguinal canal, and terminates in the spermatic cord 

 and vaginal tunic. In the female the vessel is larger and may be called 



