18 ANATOMY OF THE HORSE. 



rounded by the play over it of the obturator internus and ge- 

 melli, and at length ends insensibly in the tuberosity. — There is 

 a lesser superior border, running from the tuberosity to the 

 acetabulum, whose posterior half is prominent, very sharp, and 

 irregular, forming the ischiatic spine. 



The Inferior Border — Describes a sigmoid flexure : it extends 

 from the anterior iliac spine to the symphysis pubis. Its ante- 

 rior third is sharp ; about its middle is a medullary hole run- 

 ning backward ; here it gives rise to two borders: one obtuse 

 and smooth, ending at the edge of the acetabulum ; the other, 

 more prominent and sharp, is the linea ilio-pectinea, or brim or 

 boundary of the cavity of the pelvis, running onward to the 

 symphysis. Upon its anterior part is a rough place, the ilio- 

 pectineal eminence, marking the insertion of the psoas parvus ; 

 posteriorly are two rough eminences, with a groove between 

 them wherein run the united tendons of the psoas magnus and 

 iliacus : to the outer one, the pubic spine, is fixed the external 

 chord of the abdominal ring. 



Connection. Anteriorly and inferiorly with the sacrum ; pos- 

 teriorly and inferiorly and in the middle with each other ; out- 

 wardly with the femoral bones. 



Development. In the fcetus this bone is separable into three 

 distinctly formed pieces : — the ileum, the largest division, the 

 triangular plate in front ; the ischium, the part projecting back- 

 wards ; and the pubes, the inferior and middle portion. They 

 all contribute to the formation of the acetabulum ; the ischium 

 and pubes together form the obturator foramen. These parts 

 speedily complete their bony union after birth ; and the ischium 

 and pubes the soonest. 



OF THE PELVIS IN GENERAL. 



Division. Into exterior and interior, inlet and outlet. 



The Exterior presents — in front, the crest and anterior and 

 posterior spines of the ileum ; behind, the divergent tuberosities 

 of the ischium ; on the sides, the triangular planes of the ilea 

 which are clothed by the gluteal muscles, the acetabula, and, 

 between them and the ischiatic tuberosities, the rounded smooth 

 surfaces of the ischia, over which play the rotating muscles of 

 the haunch ; above, the sacrum ; below, the symphyses of the 

 pubes and ischia ; laterally and inferiorly, between the symphy- 

 ses and the acetabula, the foramina obturatoria. 



The Interior is divided into two compartments by a prominent 

 circumferent line forming the brim of the pelvis : the open irre- 

 gular space before this line, is the inlet or entry ; behind it, com- 



