408 DR KNOX on the Dentition of the Dugong, and on the 



10 inches. The tusk is rolled spirally throughout its whole ex- 

 tent, with the exception of about 3^ inches at the point where 

 the tusk is smooth, and resembles strongly the young teeth. On 

 looking into the cavity for the reception of the pulp, we perceive 

 the spiral twisting to be as well marked as on the outside, and we 

 find the tooth to be hollow throughout the whole extent of the 

 cavity for its reception in the jaw. With the exception of a 

 small space in the centre, we are sure that the remaining part is 

 solid. 



The animal has a distinct vertebra dentata, almost as large 

 as the atlas, and, in this respect, differs much from the com- 

 mon porpoise of the coast, which has the dentata united to the 

 atlas by bone, and not to be distinguished from it ; and the spi- 

 nous process, which is distinct, is a mere plate of bone. With 

 reference, then, to these two vertebra?, the narwal differs 

 from all the Cetacea I have examined ; and of whom it may be 

 said generally, that the vertebrae of the neck run much together, 

 and are so united as not to admit of any motion in this part of 

 the vertebral column. The neck of the narwal is therefore 

 somewhat longer proportionally than in the other whales ; and 

 the flexibility of its neck must enable it to be much more agile 

 than others of its kind. In short, we find moveable vertebra? 

 with distinct or peculiar surfaces, appearances which do not exist 

 in this part of the column in any of the other true Cetacea I 

 have seen or read of. 



There is no opening for the vertebral artery. The junction 

 of the first and second vertebrae is by two surfaces, as in man and 

 other animals. In looking into the vertebral canal, no processus 

 dentatus is seen, so that it presents an appearance as if the pro- 

 cessus dentatus had been cut slopingly off on its superior sur- 

 face, leaving only its articulating surface, as seen in other ani- 

 mals. The dentata and atlas are equal as to breadth, viz. 

 8 inches. They are almost equal as to strength. The third 



