TEETH OF MONOPHYODONTS. 



'27.1 



vol. i. p. 361, is traversed throughout by medullary canals, 

 measuring -j-Vo ^ an mcn m diameter, continued from the pulp- 

 cavity, and anastomosing in pairs by a loop, the convexity of which 

 is turned towards the origin of the tubes of the hard dentine, t. 



216 



Section of upper jaw and teeth of the Megatherium. One-third nat. size. 



The cement, ib. c, is characterised by the size, number, and 

 regularity of the vascular canals which traverse it in a direction 

 slightly inclined from the transverse axis toward the crown of the 

 tooth, running parallel to each other, and anastomose in loops, 

 the convexity of which is directed toward the hard dentine. 



The tooth of the Megatherium offers an unequivocal example 

 of a course of nutriment from the dentine to the cement, and reci- 

 procally. All the constituents of the blood freely circulated 

 through the vascular dentine and the cement, and the vessels of 



o 



each substance, intercommunicated by a few canals, continued 

 across the hard or unvascular dentine. The minuter tubes, which 

 pervade every part of the tooth, characterising by their difference 

 of lensfth and course the three constituent substances, form one 



o * 



continuous and freely intercommunicating system of strengthening 

 and reparative vessels, by which the plasma of the blood was dis- 

 tributed throughout the entire tooth, for its nutrition and main- 

 tenance in a healthy state. 



The grinding surface of the close-set molars of the Megatherium 

 differs on account of the greater thickness of the cement on their 



VOL. ITT. 



*T 2 



