REPOET ON THE SEALS. 187 



The Obturator externus in the Phocinae covers the outer surface of the obturator membrane. 

 It arises from the outer surface of this membrane, from the outer surface of the pubic bar to half an 

 inch posterior to the front of the obturator foramen, from the outer surface of the ischial bar, 

 from the outer surface of the ischial tuber, and from the anterior half of the rami of the ischium 

 and pubes, posterior to the obturator foramen. The fibres pass upwards and forwards below the 

 capsule of the' hip-joint in four slips, which are closely attached but easily distinguished. The 

 ventral or first slip comes from the pubic bar, the dorsal or fourth from the ischial bar, and the 

 other two from the surface of the large obturator membrane. It is inserted into the obturator pit, 

 and into the outer half of the posterior or dorsal border of the great trochanter to the external 

 border of the femur. The slip from the ischial bar may be looked upon as the quadratus femoris, 

 but it is indistinguishably blended with the obturator externus. This conclusion is based upon 

 the continuation upon the great trochanter of the insertion of the large obturator. 



In Macrorhinus leoninus it is very different from the former three muscles in its origin. It 

 arises in two parts. The dorsal part (or quadratus femoris) from the posterior half of the ischial 

 bar to where it turns down, from the outer surface of part of the ischial tuber, slightly from 

 the obturator membrane next the bar, and from the ischial bar posterior to the obturator 

 foramen. It is partially blended with the anterior part, and the part along the dorsal border, 

 forming a strong broad tendon, which gives off a tendinous slip from its ventral side. This slip 

 joins the adductor brevis, and is inserted along with it. The larger remaining part of the muscle 

 goes along the under surface of the neck of the femur, and is inserted into the whole of the dorsal 

 or posterior border of the great trochanter. The anterior part (or obturator externus proprius) arises 

 from the outer surface of the ischial bar from opposite the middle of the obturator foramen to 

 behind the acetabulum, from the same extent of the pubic bar, but only from its dorsal half, from 

 the obturator membrane lying next the bony origins, and from the posterior half of the concave 

 surface behind the acetabulum. It crosses the joint-capsule, and is inserted by a strong tendon 

 into the upper half of the posterior surface of the great trochanter. The insertion of this part is 

 like that of the obturator externus, while the dorsal is similar to the quadratus femoris. 



In Arctoeephalus gazella it arises from the entire outer surface of the obturator membrane ; 

 slightly from the capsule of the hip-joint ; and from the inner half of the pubic and ischial bars 

 surrounding the foramen. It passes forwards and upwards, and is inserted into the digital fossa 

 on the back of the great trochanter by a strong tendon. In Otaria it is inserted into the lesser 

 trochanter. This muscle acts as a powerful rotator of the upper end of the femur. It .rolls the 

 thigh backwards and inwards to the side of the pelvis. Humphry describes the obturatores as 

 large, and says the quadratus femoris is not a distinct muscle. I believe it is indistinguishably 

 blended with the externus in the Phocinae. 



In the Phocinte the digital pit is well marked, in Arctoeephalus it is like a groove, and in 

 Macrorhinus there is none. In the Phocinre the obturator externus covers all the ischial and pubic 

 bars and the obturator membrane to a little behind the foramen ovale. There is a slight attempt 

 at division into four slips, the slip over the pubic bar resembling the origin of the adductor longus 

 in the other Seals, and the ischial origin the quadratus femoris. In Macrorhinus the surface of 

 bone and membrane corresponding to the surface covered by the fibres in the Phocinaj is shared by 

 the obturator externus, quadratus -femoris, adductor longus and brevis. In Arctoeephalus the same 

 divisions exist but are not so simple. The muscle around and over the obturator membrane in 



