CHAP. IV] THE GENERAL ANATOMY OF GORILLA 169 



This part of the skull is ovate, longer and narrower (more dolichocephalic) 

 in the Gorilla than in either Chimpanzee or Orang-utan, longer and narrower 

 in the male than in the female Gorilla. Relatively to the facial part, it is 

 small, the reverse of the human condition thus obtaining in the Gorilla. Yet 

 the capacity is greater than in the other Simiidae. Thus Dr Oppenheirn 

 found fifteen out of twenty-two male crania with a capacity exceeding 500 c. c. 

 The average value is given as 505 c.c. (for males) and the range as from 

 420 c.c. to 585 c.c. In the adult female Gorilla, the average value is but 

 475 c.c. though individuals may attain 555 c.c. 1 The coronal suture is less 

 tortuous laterally than in its middle portion, where it meets the sagittal 

 suture. The latter is quite tortuous until the period of closure begins, when 

 the interlocking processes are reduced in length and the suture becomes sim- 

 plified and straighten The lambdoid suture is tortuous (till closure begins) 

 as far as the temporal bone (the "Asterion"), thence downwards it is straight. 

 The line of suture between the parietal and squamous bones is characteristic- 

 ally straight in its general direction, but the squamous bone overlaps the 

 parietal with long tongue-like processes. The temporal margin of the parietal 

 bone is very distinctly longer than the coronal margin, and constitute a notable 

 difference from the human skull. Wormian bones are not uncommon in 

 the sagittal and lambdoid sutures. 



The muscular ridges have already been mentioned. In a young but 

 nearly mature skull they converge rapidly from the external angular processes 

 of the frontal bone, and each divides into upper and lower lines, the upper of 

 which actually meet at the bregma though they diverge a little later. Herein 

 a conspicuous difference from aged examples is offered by the adolescent 

 Gorilla, for in the former the temporal ridges unite with one another to form 

 a great sagittally-directed crest which occupies the line of the sagittal suture, 

 and secondly, each temporal ridge combines with the corresponding portion 

 of the superior nuchal line to form a similar crest which, running coronally 

 and along the line of the lambdoid suture, is traceable at each extremity as 

 a ridge which crosses the base of the stunted but massive mastoid process to 

 join the zygoma, of which it forms the posterior root. 



The zygomatic arches themselves are strongly developed though not much 

 bowed outwardly, yet the channelling of the lateral cranial wall, especially 

 along the line of the alisphenoid, leaves a very capacious temporal fossa. 

 From the lambda, the contour-line of the skull descends sharply and obliquely 

 forwards, towards the foramen magnum, the obliquity being very character- 

 istic of the skull in all Simiidae. 



B. In the facial portion of the skull the orbits first claim attention. 

 Bounded above by a great supra-orbital ridge which is continuous from one 

 orbital margin to the other with scarcely any interruption, and which has 

 been described as resembling a " pent-house," the orbits have a somewhat 

 rectangular appearance, and though the angles are rounded off; yet the 



1 Cf. Oppenheirn, Z.fiir M. und A., Band xiv. 1911. 



