THE ATTACHMENT OF TEETH 365 



lizards, and in the poison fangs of the viperine snakes. 

 When the tooth is attached to the bone on the outer side, 

 as in Varanus, the attachment is described as pleurodont ; 

 when to the summit of the bone of attachment, as in the 

 Eel, it is spoken of as acrodont. 



(4) Gomphosis or Socketing. This is the mode of attach- 

 ment seen in human and mammalian teeth generally. The 

 tooth is implanted in a cavity in the bone forming the 

 socket, and is separated from the bone by a fibrous and 

 vascular membrane or ligament, the periodontal membrane. 



A separate socket is developed for each tooth in Mam- 

 malia, but in the Crocodile, as shown by Tomes, ' the suc- 

 cessive teeth come up and occupy a socket which is more or 

 less already in existence '. 



In this form of attachment we have the intervention of 

 a vascular membrane, and the bone of attachment is repre- 

 sented by an alveolus, which is a special process of bone 

 developed to receive the tooth, and which becomes absorbed 

 and removed when it is shed. 1 



The teeth of the rostrum of Pristis (the Saw-fish), which 

 consist of plicidentine and are of persistent growth, afford 

 an example of socketed teeth in fish, a very rare mode of 

 attachment in this class. 



1 This special development of the alveolar process is well shown in the 

 Manatee and in the Sheep, the forming teeth at the back of the mandible 

 lying in a separate tube of bone as seen in two preparations in the 

 Odontological Section of the Hunterian Museum of the Royal College of 

 Surgeons. 



REFERENCES 



1. Mummery. J. H. ' On the Teeth of Echineis.' Trans. Odontol. Soc. 



Great Brit., vol. xxxi, No. 3, p. 62. 



2. Owen, R. OdontograpJiy, p. 39, Plate xxviii. 



3. Tomes, C. S. ' Studies upon the Attachment of Teeth.' Trans. 



Odontol. Soc. Great Britain, 1874-5, vol. vii, pp. 41-56. 



