184 THE GENERAL ANATOMY OF GORILLA [SECT. A 



pollicis brevis, though by no means constant, is nevertheless 

 sometimes met with. This is another instance of a transitional 

 phase in the evolution of a series of muscles and tendons. Con- 

 versely, in Man, the M. extensor pollicis brevis may be greatly 

 reduced. In a human subject dissected at Cambridge (21. xi. 1910) 

 the remnant appeared as a mere appendage of the M. extensor 

 pollicis longus. 



7. The diaphragm is characterized by the large proportions of 

 the tendinous part, which leaves but a narrow zone of muscular 

 fibre around its periphery. The pillars of the diaphragm are 

 arranged as in Man. 



It is reasonable to suppose that this muscle has become as 

 predominant a factor in respiration as in Man. Thus for instance 

 accessory muscles of respiration, such as the scaleni, possess no 

 greater extent 1 than in the human body. In the pronograde 

 Cercopithecidae, on the other hand, they are attached to ribs 

 more caudally placed. 



8. The muscles of the hip and lower limb provide many sug- 

 gestions of the gradual approach to human conditions. A survey 

 of the muscles about to be described will shew that the essential 

 differences may be related to 



(a) The size of a muscle : ex. gr. M. gluteus maximus. 

 (6) The extension of attachment in different types : ex. gr. 

 M. gluteus maximus and M. soleus. 



(c) The position of the muscles in regard to joints, and also 

 their inclination to the axis of the limb : ex. gr. M. adductor 

 longus (primus), which in Man migrates towards the body of the 

 pubic bone. 



(d) The coalescence of muscles once separated : ex. gr. the 

 components of the M. biceps femoris and M. adductor magnus 

 (of Man). 



Some of the evidence on these points will now be given. 



The M. gluteus maximus arises from a fascia covering the 

 M. gluteus medius, from the posterior part of the iliac crest, from 

 the sacrum, greater sacro-sciatic ligament, and tuber ischii; the 



1 Kohlbrugge, op. cit., p. 43; cf. also the suggestive paper by Wood-Jones in the 

 J. A. P., Vol. xlvii. 1913. 



