298 DIGESTIVE ORGANS. [sect. 139. 



The cement is readily deprived of its earthy salts by acids, and 

 a white cartilage remains behind, which is readily separable from 

 the dentine, and furnishes, when boiled, ordinary gelatine. 



The cement, like the bones, consists of a basal substance, or 

 matrix, and lacuna, but only seldom contains Haversian canals and 

 vessels. Besides, we frequently meet with special canals, similar 

 to those of the dentine, and with other more abnormal cavities. 



The basal substance is sometimes granular, sometimes striated 

 in the transverse direction, sometimes more amorphous, frequently 

 lamellated like the bones. The lacuna? possess all the essential 

 characters of those of the bones, so that a detailed description of 



Fig. 126. 



'J 



Sk . I 1 



, 



Dentine and cement, from the middle of the fang of an incisor tooth, a. Dentinal tube ; 

 b. interglobular spaces, looking like lacuna: ; c. finer interglobular spaces ; d. commence- 

 ment of the cement, with numerous closely-disposed canals; e, lamellre of the same; 

 /. lacunae; g, canaliculi. Magnified 350 times. Of man. 



them may be omitted. Their only peculiarities are their very 

 variable number, form, and size (o'oo5'" to o'02'", even 0*03'" in 

 diameter), and the unusual number and length (up to o'C>3'") of 

 their processes. These often appear in the form of plumules and 

 pencils, and serve, when the lacunas are not isolated, both to con- 

 nect these cavities with each other, and to form anastomoses with 

 the extremities of the dentinal canals. In the thinnest part of the 

 cement, towards the crown, the lacunas are always entirely wanting. 

 They generally begin to appear towards the middle of the fang; 

 are, however, at first, few and isolated, but become more and more 

 numerous towards the extremity, and then not unfrequently lie 

 very regularly in series in the cement, just as in the outer layers 

 of the cylindrical bones. The most of their processes are directed 

 outwards and inwards, which occasions an uniform fine transverse 

 striation of the cement. 



The thick layers of cement of old teeth possess large numbers 

 of lacuna, but they are, for the most part, very irregular, and have 

 especially an elongated form. Many lacuna, either separately or 

 in groups, are half or entirely surrounded by very distinct clear 

 yellowish, slightly sinuous borders, which, perhaps, arc in some 



