THE ATTACHMENT OF TEETH 353 



brane, carrying the teeth with it, really occurs, was clearly 

 shown by the well-known specimen figured and described 

 by Professor Owen (2). In this case the jaw of a shark 

 (Galeus) was penetrated by the spine of a Sting-ray. The 

 spine entered the jaw in the region of the developing teeth 

 and the scar extended from this position to the front row 

 of the teeth in use, which showed a malformation, the result 

 of arrested development in the region of the injury. This 

 could not have occurred unless the whole of the mucous 

 membrane had been carried forward, sliding over the jaw 

 beneath (fig. 233). 



m 

 ---c 



FIG. 233. Part of the lower jaw of a Shark (Galeus) pierced by the barbed 

 caudal spine (s.) of a Sting-ray (Trygon), showing the effect of the wound 

 of the dental matrix on the teeth, which have advanced in their revolving 

 course over the jaw. m. Mucous membrane ; c. cartilaginous jaw ; a. in- 

 jured calcified teeth. 



Various modifications of the method of attachment by 

 fibrous membrane are seen in fishes. In some the attach- 

 ment admits of a very slight amount of rocking movement, 

 and transitional forms between this and true hinging are 

 met with in great abundance. 



As seen in the Eel (fig. 234), the teeth are situated on 

 little pedicles of bone, the bone of attachment, first described 

 by C. S. Tomes. This bone of attachment corresponds to 

 the alveolus of a socketed tooth ; it is developed for the 

 attachment of the tooth, and is removed or absorbed when 

 the tooth is shed. 



It has not the regular microscopic structure of the bone 



