THE GREAT CHIMPANZEE. 405 



frontal between the external angle and the prominent sinus even in the lowest Negro or 

 Australian skull : the prominence of the whole supraorbital ridge, which is the charac- 

 teristic of the genus Troglodytes, reaches its maximum in the present great species, and 

 forms the most marked distinction in the comparison of its skull with that of Man. 

 The interorbital part of the ridge, however, projects more suddenly over the root of the 

 nasal in the Ethiopian and especially Austrahan skulls than in the Chimpanzee. But 

 even in the low race of Man selected for the comparison, the development of the pros- 

 encephalon carries the interorbital part of the frontal forward so as to bring the orbital 

 cavity into view in advance of its lateral malar boundary ; but no part of that cavity is 

 seen in the same direct side view in the Chimpanzee. 



The prominent nasal bone forms part of the anterior outline below the overarching 

 frontal in Man ; but notwithstanding the characteristic projection of the nasal in the 

 great Chimpanzee, the thick swollen external wall of the orbit shuts it out of view. 

 Below the malar the alveolus of the great canine in the maxillary, and then the promi- 

 nent premaxillary and incisors, complete the anterior contour in the Chimpanzee ; but 

 in Man the concave maxillary border of the external nostril leads from the nasal to the 

 short and shghtly projecting anchylosed premaxillary bone, supporting the almost ver- 

 tical crowns of the incisors. 



The great cuspidate canine, the interval dividing it from the incisors, the superior 

 size of the first premolar over the second, the prominent double socket for the two 

 diverging external fangs of each premolar, and the equal-sized true molars, are all 

 distinctive characters in the Chimpanzee of the most decisive nature in contrast with 

 the specific peculiarities of the dentition in Man. 



In the direct side view of the human skull, a part only of the crown of the outer in- 

 cisor and scarcely any of the inner incisor can be seen projecting beyond the canine ; 

 whilst the whole crown of the outer incisor and the more prominent part of the inner 

 incisor extend beyond the canine in the Chimpanzee. The whole alveolar border of the 

 upper jaw extends much further below the base of the cranium in the Chimpanzee than 

 in Man, in whom the superior depth of the brain-case brings the mastoid process 

 almost on a level with the alveoli of the maxillary bone. The relatively shorter, deeper, 

 subquadrate form of the upper jaw is also a marked characteristic of Man. In the 

 Chimpanzee, although the alveolar border forms a right angle with the posterior border 

 of the upper jaw, the long anterior border slopes forwards towards the lower border at 

 an acute angle, and to the same degree departs from its parallelism with the posterior 

 border. 



The spheno-maxillary fissure is longer, narrower and less curved in the Chimpanzee 

 than in Man : the ectopterygoid is shorter, but the antero-posterior extent of the base 

 of this process is relatively much greater. The styliform process of the sphenoid termi- 

 nates the arch behind the pterygoid in both ; but the vaginal process with its anchy- 

 losed stylohyal is a character quite peculiar to the human skull. 



VOL. III. PART VI. 3 K 



