666 MAMMALIAN ANATOMY 



anterior union between the two innominates known as the symphysis. 

 The external surface is wide and concave in its outer part, narrow 

 and convex in its ascending part. It faces downward, forward, and 

 outward ; it gives origin to part of the quadratus femoris muscle and 

 to part of the obturator externus. 



The internal surface of the ramus of the ischium (Figs. 519, 520) 

 is similar in shape to the outer surface, but is somewhat natter, and 

 forms the lower posterior lateral wall of the pelvic cavity. The median 

 ascending part of the ramus is often marked off from the rest by a 

 ridge which crosses the surface obliquely from the median lower part 

 of the obturator foramen to the posterior end of the symphysis. The 

 part lateral to this ridge faces upward, inward, and backward, and the 

 part on its median side faces upward and backward only. A wide 

 strip of the surface along the ventral border gives origin to part of 

 the obturator interims muscle, and just within the same border, at 

 its middle, is a point of attachment for the crus penis. 



The tuberosity of the ischium lies at the posterior dorsal angle of 

 the bone (Fig. 517). It presents an external, or ventral, lip and an 

 internal, or dorsal, lip. The two lips begin at the outer side, separate 

 widely to include an intermediate surface, and then approach each 

 other and are continuous on the inner side with the ventral border 

 of the ramus (Fig. 520). The triangular posterior surface is convex 

 and rough ; since it faces upward, backward, and inward, it appears to 

 be formed at the expense of the inner surfaces of the body and ramus 

 of the ischium. It gives attachment to the origins of the following 

 muscles : to the biceps femoris at the lateral greatest swelling, then 

 to the sernitendinosus by a smaller more median area, and to the 

 semimembranosus for the rest of its extent. Its outer lip bounds the 

 area of origin of the quadratus femoris on the external surface of the 

 body of the ramus ; its inner lip bounds the dorsal part of the area of 

 origin of the obturator internus. 



The Pubes is the smallest of the three elements of the innominate. 

 It is L-shaped, and bounds the median anterior part of the obturator 

 foramen, joining the ilium and the body of the ischium above and the 

 ascending ramus of the ischium below. By its union at the symphysis 

 with the opposite pubes it forms the anterior part of the ventral wall 

 of the pelvic cavity. It may be divided into three parts, a body, a 

 horizontal ramus, and an ascending ramus. 



