22 • VERTEBRATA. 



number, 44, — neither canine nor any other tooth rising above the general level, 

 and the series is unbroken, a character now manifested only by Man. The 

 grinding surface of the molars retains the transitory and embryonic structure 

 of the ruminant type. It has some affinities with the Hog. The generic 

 name has reference to the absence of tusks, long canines, horns and claws. 

 This very perfectly preserved head is from the Eocene Gypsum Beds of Mont- 

 martre, Paris, and is now in the Garden of Plants. Size, 15 x 9. 



ORDER PROBOSCIDIA. 



The Proboscidians were formerly classed with the Ungulata, 

 with which they have many affinities, particularly in their placen- 

 tation, which, as recently discovered at the birth of an elephant 

 in Philadelphia, 1880, is non-deciduate. In some peculiar ana- 

 tomical features they approach the Rodents. 



They embrace the largest of all living terrestrial creatures, 

 and are characterized by a proboscis, incisor tusks, the absence of 

 canines, a few large transversely ridged molai-s, and pentadactyl 

 feet, indicated by the divisions of the hoof. The dorso-lumbar 

 vertebrae number twenty-three, of which twenty bear ribs. The 

 centra are extremely flattened. 



The only living Proboscidians are two species of Elephas, 

 Indicus and Africamis. The total number of teeth they develop 

 is twenty-eight ; the two permanent incisors or tusks being pre- 

 ceded by two deciduous ones. The persistent dentition of Elejphas 

 is, incisors ^:|-, canines |:^, grinders |:f=26. Mastodon had the 

 same,, excepting sometimes the possession of lowei- incisor tusks, 

 =26 or 28. Binotherkom had i \:^ c t% P f'-l m |:f=22. 



The molars of Elephas consist of vertical plates of dentine 

 covered with enamel and solidified by cementum. Those of 

 Mastodon had, as the name implies, nipple-shaped prominences 

 or tubercles. 



The molars of Ele/phas show a modification from those of the 

 Mastodon similar to the change from the Palceotherium to the 

 Horse. Occasionally a rudimentary molar is found in front, 

 which makes the typical seven. Only the last three are true molars. 

 These teeth are replaced horizontally, from behind forwards, and 

 only one or a portion of two are in use at once. The other ex- 

 treme is found in Dinotherium^ wliere all the five molars are in 

 use at once, and the milk molars are displaced vertically. The 

 Mastodon exhibits a transitional form. 



