438 CLASS MAMMALIA. 



long time was called the horn of the unicorn. 

 It has the germs of two tusks, but it rarely 

 happens that both grow equally. In general 

 that on the left side alone is developed, and the 

 other remains concealed, during the existence 

 of the animal, in the right alveolus. This small 

 tusk we have ourselves found in many crania. 

 It is not developed, in consequence of its interior 

 cavity being too speedily filled by the ivory 

 matter, and the gelatinous kernel thus becom- 

 ing obliterated. The Narwhal may be almost 

 double the length of its tusk. The skin is 

 marbled, as it were, with brown and whitish ; 

 the mouth small ; the spiracle on the top of the 

 head ; no dorsal fin, but merely a projecting 

 crest all along the spine. Some tusks of the 

 Narwhal are found perfectly smooth. 



The other Cetacea have the head so large, 

 that it makes one third, or one half the length 

 of the body ; but the cranium or brain, does 

 not partake in this disproportion, which is al- 

 together owing to the enormous developement 

 of the facial bones. 



The Cachalots (Physeter, L.) 



Are Cetacea with a very voluminous head, exces- 

 sively inflated, especially in front. No whalebone 

 in the upper jaw, nor teeth, except sometimes very 

 small ones not projecting. The lower jaw narrow, 

 elongated, and, corresponding to a furrow in the 



