CHAP. IV] THE GENERAL ANATOMY OF GORILLA 165 



notice. The tri-radius T J3 , already mentioned in connexion with 

 the Cercopithecidae (cf. supra, p. 127), has now been thrust right 

 on to the hallux : its divergent distal limbs no longer enclose a 

 figura tactilis (Fig. 104), but merely a series of transverse lines. 

 Its proximal limb (R m ) is directed first transversely and then 

 distally. Lastly the heel may now bear one or even two calcanean 

 sinuses (Fersen-sinus of Schlaginhaufen), a character scarcely known 

 in the lower Primates (though met with by Schlaginhaufen in 

 Macacus nemestrinus with a frequency of 8'5 °/„ for the single 

 sinus only). 



E. The Skeleton, (a) The skull. The first point to notice 

 in an account of the skull of the Gorilla is the great difference 

 that exists between male and female in the adult stages, and 

 between the immature skull and the corresponding mature stage 

 in either sex (cf. Figs. 105, 106). Museum specimens are most 

 frequently skulls of adult or aged male individuals ; female skulls 

 of adults, and quite immature skulls of both sexes, come next in 

 frequency, and the skulls that are the most profitable for the 

 study of the typical features of the male, viz. specimens that have 

 not quite reached maturity, and in which the permanent dentition 

 is just about to be completed, are the most uncommon. Such 

 a skull is described in detail below. Skulls of fully adult or 

 aged male examples prove unsatisfactory for two reasons : in 

 the first place, fusion of the various cranial bones is precocious, 

 and hence the relations and connexions of the several bones are 

 obscured at a comparatively early period ; secondly, with maturity 

 comes the immense development of bony ridges which indicate 

 the great mass of the temporal and nuchal muscles. These ridges 

 obscure the form of the brain-case. Equally impressive is the 

 excavation of the bone by the extension of " air-sinuses." These 

 pass principally into the region of the brow-ridges and the upper 

 jaw (Fig. 107). 



In the Gorilla, the apparatus of the jaws constitutes a factor 

 dominating every part of the skull. The growth-changes have 

 been mentioned already, and to some extent at least they are 

 illustrated by the following illustrations (Figs. 105, 106). These 

 are now supplemented by drawings (Figs. 108, 109) in which the 



