238 OUTLINES OF EQUINE ANATOMY. 



The spermatic artery is given off from the posterior 

 aorta, between the commencement of the renal and the pos- 

 terior mesenteric vessels. It is remarkable for its length 

 in proportion to its size, and for the convoluted manner in 

 which it runs through the spermatic cord. It runs in a 

 downward and backward direction to the internal ab- 

 dominal ring, where it gains the spermatic cord, in the 

 anterior part of which it passes much curled upon itself. On 

 getting near the testicle it sends off small long branches 

 to the commencement portion of the vas deferens, and on 

 gaining the antero-superior part of the organ divides into 

 two parts, one of which runs in a backward direction, the 

 other downwards until it gams the inferior margin, when 

 it also curves backwards. Both of these divisions send 

 branches into the substance of the organ which help to 

 form the tunica vasculosa. Sometimes the artery of the 

 cord is given of£ from the posterior aorta (often from the 

 external iliac). It runs to the posterior part of the cord, 

 supplying the cremaster and vas deferens. These vessels 

 are arranged as above described in the male, but in the 

 female the ovarian artery takes the place of the spermatic, 

 being much shorter and smaller in every respect. These 

 conditions, however, are reversed in the uterine artery, 

 which much exceeds its analogue the artery of the cord in 

 size, especially during pregnancy. It runs downwards and 

 backwards towards the pelvis between the two folds of 

 peritoneum which constitute the broad ligaments of the 

 uterus. 



From its upper surface the abdominal portion of the 

 posterior aorta gives off the lumbar arteries, which passing 

 upwards, give branches to the psoae muscles, others to 

 the muscles on the loins, the medullary arteries to the 

 lumbar vertebrae, and the arteries to the lumbar por- 

 tion of the spinal cord. Then the posterior aorta gives 

 off the external iliac arteries in an outward direction, 

 whereby it is much reduced in calibre, and under the 

 second sacral bone it terminates in forming the internal 

 iliacs, and sometimes the middle sacral, the former 

 running downwards and outwards, the latter directly back- 

 wards. On the right side of the posterior aorta runs the 

 posterior vena cava ; it commences beneath the anterior 

 part of the under surface of the sacrum, resulting from the 

 convergence of the common iliac veins, and in passing 



