CATARHINES. 443 



remarkable for the anterior prolongation of the base of the crown, 

 which is worn to a sharp edge by the action of the upper canine ; 

 the second premolar has a quadri-cuspid crown. The crowns of 

 the lower molars are narrower and longer than those above, especially 

 the last, in which the posterior ridge is developed into a fifth lobe 

 or tubercle. The premolars and molars of the upper jaw are im- 

 planted each by three fangs ; those of the lower jaw by two fangs. 



The smaller Baboons, of the genus Macacus, repeat on a smaller 

 scale the dental characters of the Mandrils ; but in most of them 

 the posterior tubercles of the second inferior premolar are reduced 

 to a talon or basal ridge (PI. 116, fig. 1 & 2). In fig. 3 a view is 

 given of two of the fossils from an eocene tertiary formation in 

 Sufi^olk, which have revealed the former existence of a species of 

 Macacus, in our latitudes, at that ancient period. (1) 



In the Semnopitheques (PI. 116, fig. 5) the lower incisors are- 

 more equal in size : the canines are smaller, and the upper ones less- 

 deeply grooved than in the Baboons : the base of the first lower pre- 

 molar is less extended anteriorly : the first true molar is equal to the 

 second, and the last is narrower anteriorly in proportion to its. 

 length. These dental differences, however, are very slight as com- 

 pared with those in the structure of the stomach, by the expansion 

 and sacculation of which the ordinary Semnopitheques, as well as the 

 long-nosed species {Nasica) and the thumbless species {Colobus), differ 

 from the Macacques and Mandrils. (2) 



In the long-tailed Monkeys w^ith a simple stomach {Cercopithecus) , 

 the dentition diff"ers from that of the Semnopitheques in the last 

 lower molar being quadri-tuberculate, and of equal size with the rest. 

 In the long-armed tail-less Apes, or Gibbons, {Hylobates PI. 116, 

 fig. 6) the true molars (m) are sub-equal, the lower ones being rather 

 narrower than those above ; the crowns have a more rounded contour 

 than in the inferior Quadrumana ; the upper molars support four 

 tubercles, the lower ones five, three being placed along the outer 

 curve. In the skull of an old Hylobates syndactylus, I find these 

 outer tubercles of the lower molars worn into three deep depressions, 



(1) See my " History of British Fossil Mammalia," p. 1 & 16. 



t'2) See Trans. Zool. Society, vol. i. pp. 70, and Proceedings of the Zool. Society, 1841, 

 p. 84. 



