1 6 OBSTETRICAL ANATOMY. 



more conspicuous in common than in well-bred horses, in which the croup 

 is almost horizontal, and the tail nearly on a level with its highest point. 

 The width of this region also varies not only with the height and volume 

 of the animal's body, but also according to breed : the draught or coarse- 

 bred horse having a wider croup than the thorough-bred one. This region 

 is constricted from before to behind, and shows, on the middle line, the 

 spinous processes of the sacrum and the first coccygeal vertebrae ; and on 

 each side the channels into which open the four sacral foramina. 



The inferior region is nearly horizontal, and is slightly convex. Formed 

 by the pubic and ischial bones, it offers in the middle the symphysis 

 pubis, on each side the subpubic channels, and the obturator foramen, 

 and outwardly the cotyloid cavities through which the pelvis rests on the 

 posterior limbs. 



The lateral regions are more extensive than the others ; they are in- 

 clined downwards and inwards, and are wider before than behind. On 

 each are observed the crest of the ilium and the two anterior iliac spines, 

 the external iliac fossa, the great sciatic notch, the spine of the ischium, 

 the small sciatic notch, and the tuberosity of the ischium. 



The internal surface, as has been already mentioned, is formed partly 

 of bony and partly of ligamentous walls, and circumscribes the pelvic 

 cavity, which is a continuation of that of the abdomen, and with which it 

 communicates by a wide osseous circle — the anterior opening or i7ilel 

 of the pelvis. A transverse section of this canal shows that it is oval- 

 shaped, the largest portion being towards the pubis, and the narrowest 

 to the sacrum. 



The internal surface is more regular than the external, but it cannot be 

 divided into two portions like the human pelvis, the inner aspect of the 

 ilia not being excavated to form an anterior cavity. It may, however, 

 be considered as having four co7icave planes^ an anterior opening or inlet^ 

 and 2t. posterior opening ox outlet. 



Fig. 6. 

 Longitudinal Section of the Mare's Pelvis. 



The superior, sacral, or rectal plane, or roof of the pelvis, is formed by 

 the lower face of the sacrum, and is in contact with the rectum, subsacral 

 vessels, and sympathetic nerves. It is slightly concave longitudinally. 



The inferior plane, or floor of the pelvis, is constituted by the upper 

 surface of the pubic bodies and ischia. It is rectilinear from before to 

 side to side. The symphysis pubis occupies 



