THE PELVIS. ,5 



the sacrum and coxae. It is a wide membranous expansion, composed of 

 white fibrous tissue — the fibres crossing each other in different directions, 

 and serves rather to enclose this portion of the pelvic space than to main 

 tain the solidity of the sacro-iliac articulation. It is irregularly quadri- 

 lateral ; its superior dormer being rectilinear, and attached along the rough 

 crest on the side of the sacrum, as well as to the first two or three coccy- 

 geal bones. It anterior border is irregular, and not well defined, but it is 

 inserted above into the base of the sacrum, and below into the inner 

 border of the ilium, circumscribing in its middle the opening which has 

 been named the great ischiatic notch, through which the gluteal vessels 

 and nerves, as well as the sciatic nerves, pass, and to the compression of 

 which against the bones of the pelvis during pregnancy may be due cramp 

 of the posterior limbs, or even more or less persistent paralysis ; the 

 inferior border is attached to the spine of the ischium, as well as to the 

 ischiatic tuberosity, and between these insertions, and immediately behind 

 the cotyloid cavity, it forms the small ischiatic notch, the opening through 

 which the obturator internus muscle passes j while the posterior border^ 

 not well limited, completes the posterior circumference of the pelvic 

 cavity, and divides into two layers, between which lies the semimembra- 

 nosus muscle, and above it is mixed up with the enveloping sheath of 

 the tail muscles and bones. 



The inner face of this wide ligament is covered by peritoneum to the 

 extent of one-third in front ; a-nd behind it is in direct relation with 

 various organs contained in the pelvic cavity, by means of an abundant 

 loose connective tissue. Its external face is traversed by the sciatic 

 nerves and covered by muscles. 



SECTION III. THE PELVIS AND ITS CAVITY. 



Having now studied the individual pieces which compose the pelvis, as 

 well as the manner in which they are united, it remains to consider this 

 region in its entirety, and with regard to its general conformation, dimen- 

 sions, axes, and other important features. This study is of much moment 

 in an obstetrical point of view, and for the full comprehension of the 

 mechanism of parturition. We will first notice the pelvis of the Mare 

 and proceed to compare it with the other domesticated animals. 



^ Mare. 



Considered in a general manner, the pelvis of the Mare represents 

 a slightly cone-shaped, bony cavity at the pdsterior part of the trunk, 

 completing or continuing the abdominal cavity ; the base of this conical 

 excavation, intersected obliquely downwards and backwards, is anterior : 

 its axis forming, with that of the abdomen, a very wide angle, the sinus 

 of which is inferior. The summit or narrowest part of the cavity is pos- 

 terior. With regard to conformation, it offers, for convenience of de 

 scription, an external and internal surface and tivo openings. 



External Surface. — This surface may be considered as consisting of 

 four regions, planes, or faces. The superior region or croup is the narrowest, 

 and is slightly oblique downwards and backwards : the degree of obliquity 

 varying not only in different breeds, but also in different animals of the 

 same breed and species; In the Mare it is indicated by the droop or 

 slope of the croup, which is generally greater than that of the Cow. It is 



