PROBOSCIDEA 419 
generalised outlines; and certain forms from the Eocene of North 
America, if their affinities 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 venz cave entering the 
right auricle. Stomach simple. A capacious cecum. Testes per- 
manently abdominal. Uterus bicornuate. Placenta nondeciduate 
and zonary. Mamme two, pectoral. 
With regard to the teeth, the incisors,! 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, strie 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 maxille ; 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 premaxille 
into the great and specially modified alveolar processes of the maxille, but this 
does not vitiate their homology with the incisors of other mammals. 
