264 
ZOOLOGY, 
having the cerebral hemispheres small, smooth, with none 
or few convolutions, in front not covering tlie olfactory 
lobes, and behind leaving the cerebellum wholly or partly 
uncovered. We now come to the Ediicahilia, in which the 
brain is more highly developed, the cerebral hemispheres 
being furrowed or convoluted, and partly or almost wholly 
covering the cerebrum. We begin with two very aberrant 
orders, the whales and Sirenians, in which the body is fish- 
like, though tlie tail is horizontal; the pelvis and hind 
limbs are wanting, either wholly, or minute rudiments 
may be present; and they are aquatic, occasionally leaping 
out of the water, but usually only showing the dorsal fin 
or nose when at the surface to breathe. 
The whales and porpoises have a large, broad brain, with 
numerous, complicated, and deep convolutions. 
In the skull the apertuie for the spinal cord is entirely 
posterior in situation and directed somewhat upward. The 
lower jaw is straight. The teeth are conical, wuth a sin- 
gle root, but are sometimes wanting. There is no neck; 
the cervical vertebrae are sometimes confluent, forming a 
single mass. The limbs form a pair of paddle-like append- 
ages just behind and under the head, which are supported 
by short, flattened limb-bones, the carpals and phalanges 
often separated by cartilage; the second digit being com- 
posed of more than three phalanges. There are two mam- 
mae situated near the tail. The external nostrils are either 
single or double, and are situated on the top of the head; 
they are modified to form the spiracles or blow-holes;" 
certain folds of the skin prevent the water from entering 
the air-passages. The vapor blown from the holes does 
not consist of water, but of the mucus from the nostrils, 
and the moisture in the breath. The blow-holes vary in 
form in different kinds of whales. The " spout" or stream 
of vapor issues in a single short stream from the extreme 
end of the snout, and curls over in front of the head; that 
of the fin back whale forms a single column of vapor about 
ten feet high; the right, humpback, and sulphur-bottom 
