414. CLASSIFICATION OF VERTEBRATES. 



stiff hair without a woolly fur beneath. Phoca, with incisors ^, embraces the 

 common seals of the northern Atlantic ; MonacJius (i f ) , the monk seals of 

 warmer latitudes. Cystophora (i f-) includes the hooded seals of polar seas 

 with inflatable sac connected with the nostrils. 



ORDER IX. PRIMATES. 



Diphyodont, heterodont mammals, with typically i f, m , 

 the molars usually quadritubercular ; the orbits separated from 

 the temporal fossa by a postorbital bar ; clavicles well developed ; 

 ulna and radius always distinct ; feet plantigrade, usually penta- 

 dactyl ; the pollex and (except in man) hallux opposable to 

 the other digits. The placenta deciduate or not ; diffuse or 

 discoidal. 



The primates, as a group, are not easily denned, especially 

 if the extinct forms be taken into consideration, for these to a 

 great extent bridge over the gap which exists, among recent 

 forms, between the primates and the insectivores and creodonts, 

 while in certain points there are suggestions of marsupial char- 

 acters. According to one view, the order is polyphyletic, the 

 lemurs having had one line of descent, and the monkeys, apes, 

 and man having had another ancestry. This view is based 

 primarily upon placental structures, but it is largely negatived 

 by the fossil history so far as this is known. 



SUB-ORDER i. PROSIMI/E (LEMUROIDEA). 



Arboreal primates with opposable great toe ; orbits not completely sepa- 

 rated from temporal fossa ; mammae thoracic, or thoracic and abdominal : 

 uterus bicornuate ; placenta non-deciduate, the whole surface of the chorion, 

 except one end, being covered with villi. 



The lemurs and their allies have their centre to-day in Madagascar, from 

 which outlying species extend to the African continent and to the Indian 

 archipelago, a distribution which has suggested a former continent, ' Le- 

 muria,' in the Indian Ocean. In former times their range was more extensive, 

 since abundant remains have been found in the older tertiaries of Europe 

 and North America. The living species are mostly nocturnal, and many of 

 them have the eyes peculiarly modified in accordance with their habits. In 

 addition to the characters quoted in the diagnosis it may be mentioned that 

 in some all the digits are clawed, while in others only the second and third 

 of the hind toes are provided with claws, the others bearing nails. The 

 upper molars have four or three tubercules, those of the lower jaw having four 

 or five. The brain is but slightly convoluted, and but slightly overlaps the 

 cerebellum. 



