PROBOSCIDEA 419 



generalised outlines ; and certain forms from the Eocene of North 

 America, if their attitudes are rightly interpreted, appear to link 

 the true Proboscidea to some unknown primitive type of Ungulata. 



The following are the principal characters common to existing, 

 and, by inference, to the extinct, Proboscidea. The nose extended 

 into a long, muscular, very flexible and prehensile proboscis, at the 

 end of which the nostrils are situated, and from which the name 

 given to the group is derived. The teeth consisting of ever-growing 

 incisors of very great size, but never exceeding one pair in each 

 jaw, and often present in one jaw only ; no canines ; large and 

 transversely ridged molars. No clavicles. Limbs strong, the 

 upper segment, especially in the hind limb, the longer. Radius 

 and ulna distinct, the latter articulating extensively with the carpus. 

 Fibula and tibia distinct. Astragalus very flat on both surfaces. 

 Manus and pes short, broad, and massive, each with five toes, 

 though the outer pair may be more or less rudimentary, all encased 

 in a common integument, though with distinct, broad, short hoofs. 

 Third digit the largest. Two anterior venae cavas entering the 

 right auricle. Stomach simple. A capacious caecum. Testes per- 

 manently abdominal. Uterus bicornuate. Placenta nondeciduate 

 and zonary. Mamma? two, pectoral. 



With regard to the teeth, the incisors, 1 which project largely 

 out of the mouth, and are commonly called " tusks," are of an 

 elongated conical form, and generally curved. They are composed 

 mainly of solid dentine, the fine elastic quality and large mass of 

 which renders it invaluable as " ivory " for commerce and the arts. 

 A peculiarity of the dentine of most Proboscidea is that it shows, in 

 transverse fractures or sections, striae proceeding in the arc of a 

 circle from the centre to the circumference in opposite directions, 

 and forming by their decussations curvilinear lozenges, as in the 

 " engine-turning" of the case of a watch. The enamel-covering in 

 existing species is confined to the extreme apex, and very soon 

 wears off, but in some extinct species it forms persistent longitudinal 

 bands of limited breadth. The tusks have small milk-predecessors, 

 shed at an early age. 



The molar teeth present a remarkable series of modifications, 

 from the comparatively simple form in Dinotherium, with two or 

 three strongly pronounced transverse ridges and a normal mode of 

 succession, to the extremely complex structure and anomalous mode 



1 These teeth are by some writers classed as canines, as their roots are im- 

 planted in the maxillse ; but, as in Rodents, they are originally developed in the 

 gum covering the premaxilLe, in which bones their primitive alveoli are sunk. 

 As growth proceeds, however, firm support for such massive and weighty bodies 

 can only be obtained by their roots gradually sinking through the premaxill£e 

 into the great and specially modified alveolar processes of the maxilla?, but this 

 does not vitiate their homology with the incisors of other mammals. 



