VETERINARY DENTAL SURGERT. 27 



apex of the root. The nerve fibers, which are sen- 

 sory and from the fifth pair (trigeminous), enter 

 with the blood vessels and by dividing form numer- 

 ous branches, some of which become very fine and 

 enter between the odonto blasts. Beyond this the 

 nerve fibers cannot be traced and their mode of ter- 

 mination is as yet unknown. 



The periodental membrane covers the root of the 

 tooth and is connected with the osseous alveolus, in 

 which the tooth is firmly lodged. In this membrane 

 are developed the cemento blasts which build up the 

 cementum, and also the osteo blasts which build up 

 the walls of the alveolus. In addition this membrane 

 also contains osteo clasts for the removal of portions 

 of the walls of the alveolus. This process accom- 

 modates the changes which take place during the 

 growth of the tooth. As the tooth enlarges and 

 presses on the walls of the alveolar cavity, these osteo 

 clasts absorb the walls of the alveolus, diminishing 

 its thickness in proportion to the increase in size of 

 the tooth. The osteo clasts also exert an influence 

 in shaping the roots of the teeth, or in changing 

 their form. The thickness of the membrane varies 

 very much in different animals and around different 

 teeth of the same animal. It is thickest in the 

 yoimg animal, gradually decreasing as age advances. 



The periodental membrane always closely sur- 

 rounds the root or fang and fills the alveolar cavity. 



