CETACEA. | 203 
with external, though small, openingss their viviparous genera- 
tion, the mammez with which they suckle their young, and 
all the details of their anatomy sufficiently distinguish them 
from fishes. 
Their brain is large, and its hemispheres well developed ; 
the petrous portion of the cranium which contains the internal 
ear is separated from the rest of the head, and only adheres 
toit by means of ligaments. There are no external ears, nor 
hairs upon the body. . 
The form of their tail compels tein to flex it from above 
downwards to produce a progressive motion; it also greatly 
aids them in rising in the water. 
To the genera of the Cetacea hitherto admitted, we add 
others formerly confounded with the Morses. 
FD 
FAMILY I. 
CETACEA HERBIVORA. 
The teeth of these animals have flat crowns; this determines 
their mode of life, and the latter induces them to leave the 
water frequently, to seek for pasture on shore. They have 
two mamme on the breast, and hairy mustachios; two circum- 
stances which, when observed from a distance as they raise 
the anterior part of the body vertically from the water, may 
give them some resemblance to human beings, and have pro- 
bably occasioned those fabulous accounts of Tritons and Sirens 
which some travellers pretend to have seen. Although in the 
cranium the bony nostrils open towards the top, the orifices 
in the skin are pierced at the end of the muzzle. Their 
stomach is divided into four sacs, of which two are lateral, 
- and they have a large cecum. 
Manatus, Cuv. 
The Lamantins, or rather the Manati, have an oblong body, termi- 
nated by an elongated oval fin; the grinders, eight in number through- 
out, have a square crown, marked with two transverse elevations; 
there are no incisors nor caniniin the adult; but when very young, 
we find two very small pointed teeth in the intermaxillary bones, 
