188 THE VOYAGE OF H.M.S. CHALLENGER. 



Macrorhinus has divided into three masses, the longus occupying the pubic bar and adjacent 

 membrane, the quadratus femoris, the ischial and adjacent membrane, and the obturator externus 

 the front of the obturator foramen and the pubic and ischial bars on either side. The adductor 

 brevis is isolated and is almost upon the pelvic brim, and there is a large space in the centre of the 

 obturator foramen with no fibres. In Arctocephalus the obturator externus covers all the membrane 

 and bone surrounding the foramen. The brevis is on the pubic bar and the longus is behind the 

 brevis and runs round the posterior aspect of the obturator externus to the ischial bar, while the 

 quadratus femoris is anterior to its termination. The function of this area of bone posterior 

 to the acetabulum in the Seals is to give attachment to fibres which will rotate the femur outwards, 

 adduct, and flex at the hip-joint. In Arctocephalus there are separate muscles for these various 

 movements, in addition there is an adductor magnus, and each is separately inserted into the femur. 

 In Macrorhinus there is no magnus, the brevis is insignificant in comparison with the same in Arcto- 

 cephalus, and on the femur it is receding to the obturator extensor insertion. The longus is confined 

 to the internal border of the femur, whereas in Arctocephalus it crosses obliquely the back of the 

 femoral shaft. The quadratus femoris though separate at its origin in Macrorhinus is combined 

 with the externus at the insertion. In the Phoeinre all the fibres of the externus go to the digital 

 fossa near it. Though the origins in Macrorhinus are nearly like those in Arctocephalus the insertions 

 are not, but slightly resemble those of the Phocinre as regards the quadratus and obturator externus, 

 and those of Arctocephalus as regards the brevis, and are like neither in the longus. The movements 

 of the thigh in the Phocinas are the most imperfect, and this combined mass is sufficient for them. 

 In Macrorhinus a higher stage is reached as indicated by the separation into muscle bundles, and 

 in Arctocephalus there is sufficient differentiation of the muscular mass to enable the animal to walk 

 as well as swim. 



The Gluteal Region of the Phocinae and Macrorhinus contains the gluteus maximus, medius, 

 minimus, pyriformis, obturator internus, and genielli. 



In Arctocephalus in addition to these there is the quadratus femoris. 



The Gluteus maximus in Phoca vitulina is the most superficial muscle of the gluteal region, and 

 is triangular in form. The base rests upon the vertebral spines and the apex upon the femur. 

 The dorsal head arises from the crest of the ilium between the two lips, extending from the 

 ventral anterior spine to the dorsal posterior spine; between the dorsal posterior spine and the 

 spine of the last lumbar vertebra it takes origin from the fascia covering the erector spina 1 , ami 

 also from the spines of the last lumbar, all the sacral, and the 1st caudal vertebra, by the fascia 

 which is an extension backwards of the lumbar aponeurosis, from the tendinous expansion over the 

 back of the sacrum, and from the dorsal sacro-iliac ligament. The ventral head is a narrow 

 riband-shaped fasciculus about an inch broad. It arises beneath the great division opposite the 

 level of the 3rd sacral vertebra, from the side of the dorsal sacro-iliac ligament. The fibres of 

 the dorsal division pass from their origin to the great trochanter and the external border of the 

 femur. Those coming from the crest of the iliiun go backwards to the lower and outer part of the 

 anterior border of the great trochanter. The portion lying between the dorsal posterior spine and 

 the three sacral vertebrae passes almost horizontally outwards, and the remainder between the 

 3rd sacral and the 2nd caudal go forwards and outwards to join the femur. The dorsal part is 

 inserted into the outer third of the anterior border of the great trochanter, goes obliquely 



