668 MAMMALIAN ANATOMY 



external oblique, and a prominence higher up and more or less distinct 

 affords origin for the pectineus muscle. 



The dorsal (internal) surface is concave from side to side and 

 slightly convex from above downward. It is smooth, and forms one- 

 half of the anterior transverse part of the ventral wall of the pelvic 

 cavity, affording attachment to parts of the obturator interims and 

 pubio-caudal muscles. 



The descending ramus of the pubes is the small remaining por- 

 tion which extends downward and backward from the body to meet 

 the ascending ramus of the ischium. It is wider above than below. 



Its thin and emarginate outer border bounds the obturator foramen, 

 and its thick, straight, and roughened median border joins its fellow 

 to assist in the formation of the symphysis. 



Its ventral surface (Fig. 518) slopes upward, outward, and back- 

 ward, facing downward, outward, and forward. It is smooth, and is 

 occupied by the origin of the adductor femoris and obturator externus 

 muscles. 



Its dorsal surface (Fig. 520) faces upward and backward, and 

 affords attachment to parts of the pubio-caudal and obturator internus 

 muscles. The point of junction of the descending ramus with the 

 ramus of the ischium is often marked by a tubercle on the outer or 

 obturator border. 



The acetabulum, or cotyloid cavity, is a hemispherical excavation 

 on the outer aspect of the innominate bone somewhat below the centre. 

 It is bounded by a rim, prominent throughout except at the point 

 nearest the obturator foramen, where a groove on the ischium passes 

 upward into the cavity and produces the cotyloid notch. This notch 

 is bridged by a ligament to form a canal for the passage of the vessels 

 and the nerves to the hip-joint. The walls of the acetabulum are 

 smooth, and covered with articular cartilage except at a circular space 

 at the centre of the floor, which is continued downward and inward as 

 a wide band leading to the cotyloid notch. In this region the surface 

 of the cavity is depressed and rough to give attachment to a cushion 

 of fat and also to the ligamentum teres from the head of the femur. 

 The capsular ligament of the hip-joint is attached to the innominate 

 at some little distance from the rim of the acetabulum. Of the 

 acetabulum, the ischium supplies three-fifths, the ilium one-fifth, and 

 the cotyloid bone, or pubes, one-fifth. 



