THE GREAT CHIMPANZEE. 409 



triangular plate divides the optic hole from the foramen lacerum anterius on each side, 

 which plates answer to rudiments of the ' alaj minores' and to the bases of the anterior 

 clinoid processes, but those processes are not extended backwards as in Man. The 

 foramen rotundum is closer to the foramen lacerum anterius than in Man, and the styli- 

 form foramen (st) is closer to the foramen ovale (tr). 



The mastoid bone (PI. LXIII. s m) is relatively larger, but developes a smaller and 

 more hemispheric mastoid process (m). Traces of the suture between the mastoid and 

 squamosal continue longer in the Chimpanzee than in Man. Its upper part extends 

 outwards into a strong angular ridge, and its under part extends from the process in- 

 wards as a horizontal plate (s) to join the exoccipital, which plate is of greater extent 

 than in Man, and is not grooved by the digastric muscle ; thus the space between the 

 occipital foramen (o) and the external auditory foramen (aw) is considerably greater in 

 the Chimpanzee than in Man. The stylomastoid foramen (s m) is exterior to the 

 stylohyal fossa (ss), not directly behind it as in Man, in whom the stylohyal bone be- 

 comes anchylosed at maturity with that fossa and forms the so-called ' styloid process 

 of the temporal.' There is but a rudiment of the vaginal process {v). 



The tympanic (28), which anchyloses with mastoid, squamosal and petrosal as in 

 Man, is of greater length than in Man : it forms no part of the glenoid fossa, which is 

 divided from it by the post-glenoid process, and the rudiment of the ' fissura Glaseri ' is 

 quite behind the glenoid fossa in the Chimpanzee, whilst in Man, from the different 

 relative position and shape of the tympanic or auditory process, the ' fissura Glaseri ' is 

 described as dividing the glenoid fossa transversely. The inner termination of the 

 meatus auditorius is verj^ obliquely cut off, but in a different direction from that in 

 Man ; in him it is from behind inwards and forwards, the anterior wall of the meatus 

 being longer than the posterior one. In the Chimpanzee the inner end of the meatus is 

 cut off obliquely from above inwards, downwards and forwards : at the beginning of the 

 meatus its vertical diameter is greatest, but as it penetrates the cranium the transverse 

 diameter becomes greater, the depth decreasing, and it rather suddenly expands at its 

 inner very oblique termination. 



The superior size of the parapophyses of the middle cranial vertebra* in Man relates 

 to the greater amount of muscular action required for the support and movements of 

 the skull, which is so nicely and peculiarly balanced upon the erect vertebrie of the 

 trunk : in the Quadruniana, where the skull is thrown more forwards, its support is 

 derived more from the action of the great nuchal muscles inserted into the occiput than 

 from that of the sternomastoids ; but we may infer, from the nearer approach which 

 the Troglodytes Gorilla makes to Man, in comparison with the Troglodytes niger, or with 

 the known species of Orang, in regard to its mastoid processes, that it assumed more 

 nearly and more frequently the upright attitude than the inferior anthropoid Apes do. 



* The arguments in proof of this general homology of the mastoids will be found in my work on the ' Arche- 

 type of the Vertebrate Skeleton," 8vo, pp. 29, 1 10, 120, 131. 



