The Pelvis 7 



concurs with the ilium and ischium in the formation of the ace- 

 tabuhim. 



In the mare there frequently appears a sharp elevation on the 

 median hne at the anterior end of the symphisis pubis, surmount- 

 ing the pubic brim and projecting upwards into the pelvic cavity 

 in a manner to endanger the integrity of the vaginal or uterine 

 walls when impinged between this sharp elevation while the body 

 of the fetus is passing over it under great pressure. See Fig. w^a. 

 The relations between the pelvis and the spinal column are 

 maintained by a series of ligaments and muscles. The sacro-iliac 

 articulation is very rigid, the two bones being closely applied to 

 each other by means of roughened surfaces and maintained by 

 short and very strong inter-osseous ligaments. 



The integrity of the sacro-iliac articulation is further preserved 

 behind by the sacro-sciatic ligament and in front by the pre- 

 pubian tendon and the muscles contributing thereto. 



The great sacro-sciat ic ligament arises from the t ransvers a 

 spino us ridge of the sacrum and, commencing immediately behind 

 the sac ro-iUa c ajrticulatioii, extends to the posterior extremity of 

 that bone ; passing downwards, it is attached along the supero ; 

 external border of the ijimn and i schium^ from the sacro-ihac 

 ^nk^tion, backwards to the ischial tuberosity. The two liga- 

 ments thus form wide aponeurotic sheets, which constitute the 

 greater portions of the lateral pelvic walls and occupy all that 

 area comprised between those portions of the sacrum and ilium 

 posterior to the sacro-iliac articulation and the external bor- 

 der of the ischium to the summit of the ischial tuberosity. 

 This broad and powerful ligament serves to prevent the posterior 

 portion of the pelvis or ischia from receding downwards from the 

 sacrum and affords a strong and somewhat flexible and yielding 

 wall to the pelvic cavity. It is sufficiently extensible that, under 

 the pressure of parturition, it yields enough to permit the con- 

 stricted outlet to equal in dimensions the larger bony inlet to the 

 pelvis. 



The powerful pre^ubian tendoii arises from the pubic bnm 

 and, through the linea alba and the contributory muscles, finds 

 attachment in front to the ensiform cartilage of the sternum and 

 prevents the pubis and ischium from passing upwards and back- 

 wards toward the sacral termination when the body weight is 

 thrown upon the coxo-femoral articulation, which lies behind the 



