CHAP. Ill] THE MAMMALIAN ORDER PRIMATES 47 



separate family, of which it constitutes the sole living genus and 

 species. At first its relation to the Lemuroidea was not recognized, 

 chiefly because its incisor teeth simulate those of a rodent. But 

 when its general anatomy became known, the evidence thus 

 obtained clearly shewed its affinities with the Lemurs, and with 

 these it now finds a place in classification. It is to be regarded as 

 an exceptional form of the particular lemurine type known as 

 the Indrisinae. It can be described justly as a " specialized" form, 

 though in its case specialization is compatible with, and may 

 indeed be evinced by, certain features (such as those of the brain) 

 which can only be termed " degenerate." 



SUB-ORDER 



TARSII 



Very diminutive arboreal Primates, nocturnal in habit (Fig. 20). 



Teeth : dental formula i, f ; c, -j- ; pm, § ; m, § ; the upper 

 median incisor teeth are in contact. 



Digits : provided with round sucker-like discs : nails flat save 

 on the second and third toes, which bear sharp claws. 



Orbit : a post-orbital wall is present. 



Lachrymal foramen : external to orbit. 



Hyoid bone : " lesser " cornu longer than " greater " cornu, but 

 consisting of three ossified portions with cartilaginous intervals. 



Colon : not bent as in Lemurs. 



Cerebral hemispheres : feebly convoluted ; prolonged further 

 backwards than in the typical lemurine condition ; rhinen- 

 cephalon relatively small. 



Mammae : four in number, of which two are pectoral, and two 

 inguinal in position. 



Uterus : bicornuate. 



Placenta : discoidal. 



This Sub-order comprises the genus Tarsius with two species, 

 or, it may be, varieties. These are found in a comparatively 

 circumscribed geographical area, viz. the islands of the Eastern 

 Archipelago from Sumatra to the Philippine group. The fossil 

 Anaptomorphus found in North America is considered to be nearly 

 related to Tarsius. 



