96 THE BONES. 



Tie inferior region is nearly horizontal. Formed by the pubes and ischia, 

 it presents from before to behind : 1, In the middle, the ischio-pubic 

 symphysis; 2, On each side the subpubic groove, the oval foramina, and 

 the inferior face of the ischia ; 3, Quite externally, the cotyloid cavities, by 

 which the pelvis rests on the posterior limbs. 



The lateral regions are oblique from above to below and within to 

 without, and wider in front than behind. They exhibit : 1, The spine of 

 the ilium and the two anterior spinous processes; 2, The external iliac 

 fossa ; 3, The isohiatic arch ; 4, The supercotyloid crest or ischiatic spine, 

 which presents outwardly the surface of insertion for the internal or deep 

 gluteus muscles ; 5, The lesser ischiatic notch ; 6, The ischiatic tuberosity. 



In'ernal surface.— The internal surface of the Horse's pelvis cannot be 

 divided into two portions as in Man, because the inner aspect of the iliac bones 

 is not hollowed out to form an anterior cavity. 



The pelvis of Solipeds is, therefore, a simple conoid cavity, in which are dis- 

 tinguished four regions or faces, and two apertures called the inlet and outlet. 



The anterior opening or inlet is nearly circular, especially in the Mare, 

 and a little oblique downwards and backwards. It is limited above by the 

 inferior face of the base of the sacrum ; inferiorly, by the anterior border of 

 the pubis : and on the sides by a portion of the inner face of the iliac bones, 

 and also the internal aspect of the pectineal crests. 



The inlet presents four diameters : a vertical, horizontal, and two 

 oblique. The first extends from the inferior face of the sacrum to the 

 anterior border of the pubic symphysis ; its mean length is Si inches. 

 The second is measured from one pectineal crest or eminence to another ; 

 the mean of this is 8^^ inches. The two last diameters are estimated from 

 ihe inferior face of the sacro-iliac articulation of one side to the ilio-pectineal 

 eminence of the other ; this is on an average Sy"^ inches. These measurements 

 irrefutably demonstrate that the inlet is not elliptical in the vertical direction. 



The posterior aperture or outlet, situated at the posterior end of the pelvic 

 cavity, gives exit to the rectum and genital organs. As the pelvis of the 

 horse is horizontal, the outlet should be considered as limited, we think, by 

 the inferior face of the summit of the sacrum, the superior face of the ischia, 

 the supercotyloid crest or ischiatic spine, and the internal face of the 

 sacro-ischiatic ligaments. At the outlet only two diameters are recognised : 

 a vertical and a horizontal. The vertical measures on an average 6^-^ inches ; 

 it extends from the inferior face of the sacrum to the superior face of the 

 ischial symphysis. The horizontal diameter, comprised between the two 

 supercotyloid crests, is 7-^ inches. 



The superior region of the pelvic cavity is a little concave from before 

 to behind ; it has for base the sacrum, which presents on each side of the 

 median line the subsacral foramina. This part is also called the sacral 

 plane or roof of the pelvis. 



The inferior region, or ischio-pubic plane, is formed by the pubis and 

 the ischia. It is concave from side to side ; its anterior border is nearly 

 straight, and its posterior border is scooped out by a wide notch to form the 

 arch of the ischium. 



It has been remarked by M. Gobaux, that the portion of this plane corre- 

 sponding to the pubis presents numerous varieties. The superior face of the 

 pubis may be convex in its anterior moiety and concave in its posterior ; or 

 it may be concave before and convex behind, the concavity being separated 

 from the convexity by a transverse ridge. This ridge is sometimes represented 

 by a series of small conical eminences , at other times this upper face is 



