16 



In the greater relative size of the molars, compared with the inci- 

 sors, the Gorilla makes an important closer step towards Man than 

 does the Chimpanzee. The molar teeth are relatively so small in the 

 Siamang, that, notwithstanding the small size of the incisors, the 

 proportion of those teeth to the molars is only the same as in the 

 Gorilla : in other Gibbons (Hylobates lar), the four lower incisors 

 occupy an extent equal to that of the first four molars, in the Chim- 

 panzee equal to that of the first three molars, in the Siamang equal 

 to that of the first two molars and rather more than half of the third, 

 in Man equal to the first two molars and half of the third : in this 

 comparison the term molar is extended to the bicuspids. 



The proportion of the ascending ramus to the length of the lower 

 jaw tests the relative affinity of the tailless apes to Man. 



In a profile of the lower jaw, the author compares the line drawn 

 vertically from the top of the coronoid process to the horizontal length 

 along the alveoli. In Man and the Gorilla it is about -^ths, in the 

 Chimpanzee y^-ths, in the Siamang it is only y%ths. The Siamang 

 further differs in the shape and production of the angle of the jaw, 

 and in the shape of the coronoid process, approaching the lower Simice 

 in both these characters. In the size of the post-glenoid process, in 

 the shape of the glenoid cavity which is almost flat, in the propor- 

 tional size of the petrous bone, and in the position of the foramen 

 caroticum, the Siamang departs further from the human type, and 

 approaches nearer that of the tailed Simice, than the Gorilla does, 

 and in a marked degree. 



Every legitimate deduction from a comparison of cranial charac- 

 ters makes the tailless Quadrumana recede from the human type in 

 the following order : — Gorilla, Chimpanzee, Orangs, Gibbons, and 

 the last named in a greater and more decided degree. 



These comparisons have of late been invested with additional 

 interest from the discoveries of remains of quadrumanous species in 

 different members of the tertiary formations. 



The first quadrumanous fossil, the discovery of which by Lieuts. 

 Baker and Durand is recorded in the * Journal of the Asiatic 

 Society of Bengal,' for November, 1836, has proved to belong, like 

 subsequently discovered quadrumanous fossils in the Sewalik (pro- 

 bably miocene) tertiaries, to the Indian genus Semnopithecus. The 

 quadrumanous fossils discovered in 1839, in the eocene deposits of 

 Suffolk, belong to a genus (Eopithecus) having its nearest affinities 

 with Macacus, The monkey's molar tooth from the pliocene beds 

 of Essex is most closely allied to the Macacus sinicus. The remains 

 of the large monkey, four feet in height, discovered in 1839 by 

 Dr. Lund in a limestone cavern in Brazil was shown by its molar 

 dentition (p ^> jj^jj ) to belong to the platyrrhine family now 

 peculiar to South America. The lower jaw and teeth of the small 

 quadrumane discovered by M. Lartet in a miocene bed of the South 

 of France, and described by him and De Blainville, are so closely allied 

 to the Gibbons, as scarcely to justify the generic separation which 

 has been made for it under the name Pliopithecus. 



