THORAX AND ABDOMEN OF THE HORSE 157 



defect, the lesser sciatic foramen, occurs between the ischium and the 

 sacro-tuberous ligament. The ventral wall is formed by the ilia and 

 the ischia, and is entirely bony except at the obturator foramina. The 

 outlet or caudal pelvic aperture may be described as triangular in 

 form, with a blunt apex at the second coccygeal vertebra and a base 

 formed by the sciatic arch of the ischia. The outlet of the pelvic 



Lig. sacroiliacum ventrale. 



M. longissimus dorsi. 



AI. obliquus intcrnus 

 abdominis. 



^ M. obturator internus. 



M. psoas minor 

 M. rectus femoris 



M. levator ani 

 Conjoint tendon of abdominal muscles 



Fig. 68. — Cranial aspect of the hip-bone and sacrum, with areas of 

 nmscular attachment. 



cavity, being smaller than the inlet, is of importance in obstetrics in 

 that its lateral boundaries are ligamentous and not bony. The thin 

 and not very definite caudal border of the sacro-tuberous liga- 

 ment, to which is attached the semimembranous muscle, stretches 

 from the second coccygeal vertebra to the sciatic tuber of the 

 ischium. 



The contents of the pelvic cavity differ with the sex, 

 but it is convenient to suppose that the subject being dissected 

 is a male. The contents of the female pelvis will be considered 

 later. 



