12 OBSTETRICAL ANATOMY. 



SECTION III.— THE PELVIS AND ITS CAVITY. 



Having now studied the individual portions 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 con- 

 formation, dimensions, axes, and other important features. This study 

 is of much moment from an obstetrical point of view, and for the full 

 comprehension of the mechanism of parturition. 



The cavity of the pelvis is the space between the inlet and outlet. 

 In the human female it lodges nearly the whole of the uterus, and in 

 the early days of pregnancy the foetus also. This is not the case with 

 the domesticated animals, owing to their different attitude, until the 

 act of parturition carries the progeny there.^ With its two openings, 

 the pelvic cavity is capable of more or less increase in capacity in 

 every direction, through relaxation of the pubic and sacro-iliac articu- 

 lations and sacro-sciatic ligaments. The yielding of the latter is very 

 noticeable in the larger animals immediately before parturition, as well 

 as the elevation of the coccyx by the body of the foetus in its passage 

 outwards. It is also a fact of daily observation that the pelvis per- 

 manently widens in animals which have had young frequently ; this 

 accounts for the peculiar rocking gait they exhibit in progression, which, 

 in some of the domesticated creatures at least, is no doubt due to per- 

 sistent relaxation in the articulations above mentioned. 



It may be again observed that the anterior margin of the floor of this 

 cavity is nearly straight, and its posterior border is deeply cut into by 

 the ischial arch, while the floor itself often offers some diversities. 

 For instance, it may be convex in front and concave behind, or vice 

 versa, the concavity being separated from the convexity by a transverse 

 ridge, which may also be represented by a series of small conical 

 eminences ; or the floor may be a smooth plane sloping upwards from 

 before to behind, with a kind of raised border surrounding the anterior 

 contour of the obturator foraiuen. 



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 posterior part of the trunk, 

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

 space, intersected obliquely downwards and backwards, is anterior : 

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

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

 posterior. With regard to conformation, it offers, for convenience of 

 description, an external and internal surface, and tico openings. 



External Surface. — This surface may be considered as consisting 

 of four regions, j^lcines, 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 



^ Girard thought that, in the Bitch, one of the young in the body of the uterus might 

 occupy this space ; but Rainard could not verify this : all his examinations of prej^nant 

 animals which had died before bringing forth their young proved the body of the uterus 

 to be quite empty. 



