7S3 



orbital wall?, and of the inferior tumid malar boundaries of the orbits. But the decisive spe- 

 cific character is given by the form and connections of the nasal bones : these have coalesced 

 together in Tr. Gorilla as in Tr. niger, but less completely, a linear indication of the median 

 suture remaining along the exterior surface : the coalesced upper portions of the nasals 

 ascend higher above the nasal processes of the maxillary than in Tr. niger, become contracted 

 between those processes and there project slightly, their median coalesced margins being in- 

 clined forwards, and thus offering a feature of approximation to the Human structure, which 

 is very faintly indicated in the skull of the Tr. niger (No. 5087). The nasal bones in the 

 larger species expand at their lower halves, terminate in a slight point below, and articulate 

 laterally not only with the maxillary bones, but with an expanded superior portion or dis- 

 memberment of the premaxillaries. A considerable extent of the sutures uniting these bones 

 with the maxillaries remains in the Tr. Gorilla, but they are obliterated in the Tr. niger. 



In the specimen of the skull of the immature Tr. niger (No. 5171), with only the twenty 

 deciduous teeth in place, the maxillo-premaxillary sutures, still traceable at the sides of the 

 nasal aperture as well as on the palate, show that each premaxillary bone terminates above iu 

 a point which does not reach the nasals. The inferior or alveolar part of the premaxillaries 

 is shorter and less prominent in Tr. Gorilla than in Tr. niger, and in that respect the larger 

 species deviates less from Man. The anterior surface of the premaxillaries is more irregular 

 or undulated by the prominent sockets of the incisors in Tr. niger than in Tr. Gorilla. The 

 nostril is a wider and more regular ellipse in Tr. Gorilla ; it is contracted above in Tr. niger, 

 which gives it an ovate form with the great end downwards, and thus it more resembles the 

 form of that aperture in Man. 



The orbits have a more subquadrate form, with the angles rounded off, in Tr. Gorilla than 

 in Tr. niger ; but their periphery is less sharply defined, especially below, than in Tr. niger. 

 The sethmoidal cells are more swollen out, giving the interorbital space a greater breadth 

 below and the lacrymal fossae a more anterior aspect in Tr. Gorilla. 



The infraorbital canal is open from its posterior commencement to where it perforates the 

 lower border of the orbit, and it issues upon the face relatively lower and further from the 

 orbit in the Tr. Gorilla. The whole nasal bone is relatively longer, and the distance from 

 the orbits to the external nostril greater in the Tr. Gorilla. The malar bone is more convex 

 outwardly, and is more remarkable for its vertical extent : it is flatter and developed more 

 transversely in the Tr. niger. The larger proportional size of the canines in Tr. Gorilla im- 

 presses a corresponding difference upon the alveolar part of the maxillary bone in that species. 



In comparing the skulls of the two species by a view of their base, the first remarkable 

 difference is the broad, flat, or slightly concave superoccipital surface of the larger species as 

 compared with the uniformly convex character of the same part in the Tr. niger : the differ- 

 ence is due to the much thicker and broader lambdoidal ridge in the larger species, which 

 prolongs the surface far beyond the cerebellar fossa, and gives the condyles and foramen mag- 

 num a rather more advanced position as compared with the Tr. niger. The next character, 

 which is also a more anthropoid one, though explicable in relation to the greater weight of 

 the skull to be poised upon the atlas, is the greater prominence of the mastoid processes in 

 the Tr. Gorilla, which are represented by only a rough ridge in the Tr. niger. These pro- 

 tuberances are cellular, and with a very thin outer layer of bone in the Tr. Gorilla. The 



