THE PROBOSCIDIANS. 597 
Period a fossil Sirenian (Halitheriwm) inhabited the shores 
of western Europe. 
In the structure of the skull, their dentition and their her- 
bivorous habits the Sirenians in a degree connect the Ceta- 
ceans with the Ungulates, and elephants. 
Order 7. Proboscidia.—Only two representatives of this 
group are now in existence, the Asiatic and African elephant, 
a number of other forms having become extinct. The group 
is well circumscribed, when we consider the living species, 
but in the early (Eocene) Tertiary Period there existed forms 
which indicate that the Proboscidians and Ungulates had a 
common origin. In 
the elephants the up- 
per incisors are enor- 
mously developed, 
while there are none 
in the lower jaw. 
There are no canine 
teeth, while the few 
molars are large, trans- 
versely ridged. In the 
elephants the ridges 
are numerous, the 
spaces between them 
filled with cement. 
The young mastodon 
has cement on the up- 
per surface of the | Dineen 4 aan 
tooth ; the ridges af- diiare borccatatuine the moat Ane Oke, &; 15, 
terwards become free errr ete re ee aire iiss aa mopee 
and covered with a fit uae tea ats maxilla ; 11, frontal; g, 
enamel. A peculiari- 
ty in the elephant’s skull is its large size, the brain cavity 
being very small in proportion to the bulk of the skull itself. 
To give lightness to what would be otherwise an insupportable 
weight, the cranial bones contain numerous large air-cells 
. (Fig. 520). Another remarkable feature,from which the group 
takes its name, is the trunk or proboscis, a long, thick, fleshy, 
flexible snout, growing from the front edge of the nasal 
, 
