THE DENTAL TISSUES. 97 



cavities, elongated in the direction of the lamellae of the 

 matrix, and furnished with a large number of processes. 

 The processes of the lacunae (known as canaliculi) are most 

 abundantly given off" at right angles to the lamellae (see 

 Fig. 51), and, again, in cementum, are more abundantly 

 directed towards the exterior of the root than towards the 

 dentine. The lacunae of cementum differ from those of 

 bone in being far more variable in size, in form, and in the 

 excessive number and length of their canaliculi ; in this 

 latter respect the lacunae of the cement of Cetacean teeth are 

 very remarkable. 



Many of the lacunae in cementum are connected, by means 

 of their canaliculi, with the terminations of the dentinal 

 tubes (Fig. 52) ; they, by the same means, freely intercom- 

 municate with one another, while others of their processes 

 are directed towards the surface, which, however, in most 

 instances, they do not appear to actually reach. 



The lacunae assume all sorts of peculiar forms, especially 

 In the thicker portion of the cement. 



Here and there lacunae are to be found which are fur- 

 nished with comparatively short processes, and are contained 

 within well-defined contours. Sometimes such a line is to 

 be seen surrounding a single lacuna, sometimes several 

 lacunae are enclosed within it ; lacunae so circumscribed are 

 called " encapsuled lacunae," and were first observed by 

 Gerber in the cement of the teeth of the horse (they are 

 specially abundant in the teeth of the solidungulata). By 

 cautious disintegration of the cementum in acids these en- 

 capsuled lacunae may be isolated ; the immediate walls of 

 the lacunae and canaliculi, just as in bone, being composed 

 of a material which has more power of resisting chemical 

 re-agents than the rest of the matrix. 



The encapsuled lacunae are to be regarded as individual 

 osteoblasts, or nests of osteoblasts, with a common connective 



H 



