16 



ed animal an approach to cuspidation in the shape of a distinct 

 thickening of the basal ridge. 



This is also to be seen in varying degree in Cebus capucinus, 

 Cercopithecus Diana and in the lower jaw only in Cynocephalus niai- 

 mon, Mustek furo, M. vulgaris and M, putorius. The upper canine 

 of Pteropus medius and both upper and lower in Plecotus auritus show 



Fig. V. 



a low cusp. Finally in Hapale Jacchus (Fig. V) there is a very distinct 

 lingual cusp equal in size to that of the first bicuspid. 



Incisors. Two distinct stages can also be observed in the for- 

 mation of a lingual cusp in these teeth. These are firsthly a raising 

 of the basal ridge so that the posterior triangular surface is slightly 

 elevated on its lingual aspect , in fact, accentuation of the basal ridge 

 together with a slight deepening of the cavity of the crown (Fig. II h.). 

 The second stage is an elevation of a part of the basal ridge into a 

 small tubercle so as to form a cusp (Fig. Ill f. Fig. IV all incisors). 

 The first stage can be seen in Cercopithecus Diana (especially lower 

 teeth), in Canis familiaris (upper), C. vulpes outer incisor (upper and 

 lower), Meles taxus, Mustela furo, M. vulgaris and M. putorius (all upper 

 outer) as also in Pteropus medius and Plecotus auritus. It is more 

 marked in Cebus capucinus especially in the upper outer incisor where 

 the elevation almost produces a cusp. The accentuation is less mark- 

 ed in this form in the upper central and still less in the lower. 

 In Hapale Jacchus (Fig. V) a distinct lingual cusp is present in the 

 lower lateral and an elevated cingulum in the other incisors. In 

 Sorex tetragonurus the edge of the lower incisor is norched; the large 

 upper incisor appears bifurcate from the great development of the 

 posterior talon. (Owen, Odontol. p. 417.) 



