226 THE CRANIA OF THE SIMIIDAE (PRIMATES) [SECT. A 



seen projecting into the maxillary antrum, along the roof of which 

 the infra-orbital nerve runs in a bony canal. In the Orang-utan, 

 the part of the frontal bone, which is excavated by the air-sinuses 

 in die other apes, is a solid mass which may attain a thickness 

 of nearly 20 mm. : seen in section, this thickness is reduced to 

 about a quarter of that amount at the coronal suture, and the 

 latter dimension is retained to the region of the lambdoid suture, 

 where it is increased by the ridge which crosses the skull in 

 a position corresponding to the lambdoid suture in man. 



In contrast to the human skull, the bones of the cranial vault 

 thus form an arch of much less bold proportions, and this is 

 perhaps most noticeable at the occipital end of the skull, which 

 gives the impression of having been arrested in development, 

 leaving the occipital arc but slightly curved, and the foramen 

 magnum consequently midway between the posterior and the 

 inferior aspects of the skull. Again, the greatest longitudinal 

 diameter measured from the glabellar point on the brow-ridges 

 (or between them), passes to the external occipital protuberance 

 in the crania of most apes 1 . The skull of the Orang-utan (cf. 

 Fig. 149) may provide a second point equidistant from the brow, 

 but below the external occipital protuberance. In the vast majority 

 of human crania, the diameter of greatest length ends posteriorly 

 at a point above the external occipital protuberance. The ex- 

 ceptions include certain prehistoric crania, notably that from the 

 Neanderthal. The latter is " simian " in this respect. 



On the endocranial surface, only faint impressions mark the 

 former positions of the cerebral convolutions 2 . Grooves for the 

 lateral sinuses (of the dura mater) diverge symmetrically from 

 the torcular in the mesial plane, and are of equal size, the lack of 

 symmetry (usually due to the preponderance of the sinus on the 

 right side, and associated with right-handedness) found in human 

 crania being absent here. The superior petrosal sinus may be 

 almost completely roofed-in by bone, a bony bridge may be formed 

 over the Gasserian ganglion, and the anterior clinoid process may 



1 Cf. Schwalbe 1901. Bonner Jahrbilcher; also Verhandlungen der deutschen 

 anatomischen Gesellschaft in Anat. Anz. 1901. Versanimlung, Bonn. 



- Cf. Schwalbe's description of the disposition of the endocranial impressions 

 [Zeitschrlft fiir Morphologie uml Anthropologic, Band vn. 1904). 



