264* OUTLINES OF EQUINE ANATOMY. 



the internal surface of vastus internus on the other, then 

 dips between the two portions of the large head of biceps 

 adductor. Thus it gains the posterior part of the femur, 

 and after giving off a large branch running directly hade- 

 wards, passes between the internal head of gastrocnemius 

 externus and gastrocnemius inter nus. 



After giving off the external iliac arteries, the posterior 

 aorta becomes very small in calibre, and after running 

 about two inches on the under surface of the sacrum, 

 breaks up to form two internal iliac arteries, between 

 which is sometimes seen the middle sacral artery. The 

 internal iliacs diverge, running in a downward, outward, 

 and backward direction, giving off the artery of the hulb, 

 and termina^te by breaking up into the obturator, gluteal, 

 and lateral sacral trunls. The artery of the bulb, almost 

 at its origin gives off the umbilical artery, which, pervious 

 in the foetus, in the adult degenerates into an impervious 

 fibrous cord, w^hich runs to the central part of the fundus 

 of the bladder between the two folds of the broad liga- 

 ment of that organ. It is termed the round ligamerit of 

 the bladder, and in the foetus serves to carry blood to the 

 chorion for revivification. After giving off this vessel the 

 artery of the bulb passes along the side of the pelvis, gives 

 off a large branch to supply the bladder and prostate gland, 

 and terminates in the bulb of the penis ; in the female in 

 the erectile walls of the vagina. It gives off perineal 

 branches, which supply the posterior part of the rectum 

 and the anus, anastomosing with branches from the lateral 

 sacral and internal puclic arteries. 



The obturator runs from its origin directly over the 

 venter surface of the ilium to the anterior and external part 

 of the obturator foramen, after passing through which it 

 breaks up into three very indefinite branches : pmbic runs 

 forwards, ischiatic downwards, and the internal pudic to 

 the bulb of the penis, breaking up in the erector penis 

 muscle, and anastomosing anteriorly with the posterior 

 dorsal artery of the penis, given off by the external pudic 

 branch of the epigastric, posteriorly with the artery of 

 the bulb. While pa'ssing over the surface of the ilium, the 

 obturator gives off a branch which passes over the brim of 

 the pelvis just above the origin of rectus femoris, and 

 passes mainly between that muscle and vastus externus ; it 

 is the arteria innominata. 



