SEVERAL EXTINCT SUB-ORDERS. 765 
molars are very large, and the enamel is very much plaited, 
forming a series of transverse ridges enclosing the dentine, 
and united to one another by cement. Thus on the worn 
tooth there are numerous successive layers of enamel, 
dentine, and cement. Extinct forms show transitions 
between this complex type and the hoise’s tooth. In a 
lifetime there may be six molar teeth on each side of each 
jaw, but of these only one, or portions of two, can find 
Space at a time. The series gradually moves forward as 
the front parts are worn away and cast out. 
The brain is highly developed. 
The stomach is simple, and there is a large caecum, 
There are two superior venz cave entering the right 
auricle. The kidneys have several lobes, separated by 
muscular partitions. 
The testes remain abdominal in position. 
There are two pectoral mammee ; the uterus is bicornuate ; 
the placenta is non-deciduate and zonary. 
Elephas, es now represented by the Indian Elephant (£. zzdzcus), 
with parallel folds of enamel on the molars, and ears of moderate size, 
and the African Elephant (2. afrdcanus), with lozenge-shaped folds of 
enamel, and very large ears. 
The mammoth (Z. przmigenzus) belonged to the Pleistocene period, 
and had a wide geographical- range, occurring, for instance, in 
Britain. 
The genus Mastodon is represented by fossil remains in Miocene, 
Pliocene, and even in Pleistocene strata, in Europe, India, and America. 
The molar teeth show transitions between those of elephants and those 
of other Ungulates. 
In Dinotherium, found in Miocene and Pliocene strata in Europe 
and Asia, the lower jaw bore an enormous pair of tusks projecting 
vertically downwards, and all the back teeth seem to have been in use 
at the same time. 
SEVERAL EXTINCT SUB-ORDERS 
Although we cannot describe the following remarkable types, it is 
important to notice their existence, for they serve to impress us with 
the original connectedness of what are now separate orders. 
The huge Amblypoda, in Eocene formations in America and Europe, 
had usually remarkable protuberances on the top of the skull, a very 
small brain, large upper canines, especially in the males, and six back 
teeth. : 
Example.— Uintatherium (Dinoceras), with no upper incisors. 
Some Tertiary American forms, e.g. Zoxodon and Nesodon, varying 
