96 A MANUAL OF DENTAL ANATOMY. 



plex-patterned crowns of the teeth of ruminants ; and, in 

 my opinion, is present in a rudimentary condition upon the 

 teeth of man, &c., as Nasmyth's membrane. The cementum 

 is the most external of the dental tissues : a fact which ne- 

 cessarily follows from its being derived more or less directly 

 from the tooth follicle. 



Both physically and chemically, and also in respect of the 

 manner of its development, the cementum is closely allied 

 to bone. It consists of a calcined matrix or basal substance, 

 to a slight extent laminated, and lacunas. Vascular canals 

 corresponding to the Haversian canals of bone, are met with, 

 but it is only in thick cementum that they exist ; and, in 

 man, perhaps in exostosis more often than in the thick 

 healthy tissue. 



The matrix is a calcined substance, which, when boiled 



yields gelatine, and if decalcified retains its form and struc- 

 ture : it is, in fact, practically identical with the matrix of 

 bone. It is sometimes apparently structureless, at others 

 finely granular, or interspersed with small globules. 



The lacunae of cementum share with those of bone the 

 following characters: in dried sections they are irregular 



( l ) Lacuna of cementum which communicates with the terminations of 

 the dentinal tubes. 



