CHAP. IV] THE GENERAL ANATOMY OF THE TARSI1 



105 



4. The nasal duct is placed on the facial surface and entirely 

 outside the orbital cavity. This denotes extensive development 

 of the " pars facialis " of the lachrymal bone. 



A review of the cranial characters of Tarsius indicates that 

 features of specialization are the more prominent. These are 

 most easily intelligible if regarded as adaptations to particular 

 conditions. A few suggest the derivation of the higher cranial 

 type of the Anthropoidea. As for primitive features, they are 

 probably most distinct in the system to which a few words must 

 now be devoted, viz. the dentition. 



As a whole, this is decidedly primitive or achaic 1 in Tarsius 

 (Figs. 58 and 59). There is no gap (between the upper incisor 

 teeth) such as that which is so distinctive of the Lemurs. Moreover 

 the incisors are not pro-cumbent, but erect, and the series of small 

 sharply-pointed conical teeth in the front of the mouth (extending 

 to the first premolars inclusive) produces a strong resemblance to 

 the dentition of the Insectivora 2 . The upper molar teeth bear three 

 cusps only, while in the lower molars, the three cusps are supple- 

 mented by a "heel" or "talon" (for further details cf. Chapter vi). 



The two halves of the mandible are joined by synostosis at the 

 mental symphysis, and thus the condition found in the Anthro- 

 poidea is recalled. 



Vertebral Column. A skeleton of Tarsius spectrum in the 

 Cambridge Collection has the following vertebrae, viz. total 49, of 

 which 7 are cervical, 13 thoracic (according to Burmeister, 14 

 thoracic vertebrae may occur), 6 lumbar, 5 sacral and 18 caudal 

 in character. 



The atlas vertebra is characterized by its great size and more 

 particularly by its width. Of the cervical vertebrae, the second or 

 axis alone presents a distinct (though not a bifid) vertebral spine. 

 These peculiarities may provide an explanation of the extent of 

 rotation of which the head (in the living animal) is capable as 

 described above. 



The six lumbar vertebrae are arranged in a perfectly recti- 

 linear series, but a distinct lumbo-sacral angle is observed in 



1 Hubrecht, Descent of t lie Primate*, 1897, p. 11. 



- Earle, Natural Science, May, 1897, p. 309: with special reference to the work 

 of Leche. 



