264 ZOOLOGY. 



having the cerebral hemispheres small, smooth, with none 

 or few convolntiuns, in front not covering the olfactory 

 lobes, and bohintl leaving the cerebellum wholly or partly 

 uncovered. We now come to the Educahilia, in which the 

 brain is more highly developed, the cerebral hemispheres 

 being furrowed or convoluted, and partly or almost wliolly 

 covering the cerebrum. We begin with two very aberrant 

 orders, the whales and Sii'enians, in which the body is fish- 

 like, though the tail is horizontal; the -pelvis and hind 

 limbs are wanting, either wholly, or minute rudiments 

 may be present; and they are aquatic, occasionally leajting 

 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 aperture for the spinal cord is entirely 

 posterior in situation and directed somewhat upward. The 

 lower jaw is straight. The teeth are conical, with a sin- 

 gle root, but are sometimes wanting. There is no neck; 

 the cervical vertebriB are sometimes confluent, forming a 

 single mass. The limbs form a pair of paddle-like append- 

 ages just behind and under the head, which ai'e supported 

 by short, flattened limb-bones, the carpals and ])lialangcs 

 often separated hj cartilage; the second digit being com- 

 posed of more than three j)lialanges. There are two mam- 

 mae situated near the tail. Tlie external nostrils are eitlier 

 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-liolcs vary in 

 form in diiferent 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 finback wliale f(irms a single column of vapor about 

 ten feet high; the right, humpback, and sulphur-bottom 



