174 



OSSEOUS SYSTEM. 



[SECT. 91. 



transversely cut canaliculi, without tlieir appertaining lacunae, 

 which gives rise to a cribriform appearance (fig. 79, a). The 

 innermost lacunas of a Haversian system send all the canaliculi 



Fig. 79. 





—a, 



Section from the parietal bone. Lacunae with the canaliculi seen from the surface ; 

 magnified 450 times. The points upon the cavities, or between them, belong to the 

 cut canaliculi, or are the openings of the latter into the lacuna;, a a. Groups of trans- 

 versely cut canaliculi, each belonging to a lacuna which has been destroyed in the 

 preparation of the section. 



arising from their inner surface to the Haversian canal, into 

 which they thus open. From the borders and from the outer 

 surface other canaliculi arise, which, perhaps, occasionally ter- 

 minate in blind extremities, but chiefly anastomose with those 

 of the neighbouring, and more especially of the outer lacunae. 

 Thus, whilst all the successive lacunae are connected with each 

 other, the network of canaliculi and lacunae extends to the outer- 

 most lamella of the system, where the lacunae are either connected 

 with those of neighbouring Haversian systems or of intermediate 

 lamellae, or end without further connexion. In the latter case, 

 all, or at least the majority and the longest of tlieir canaliculi, 

 proceed inwards, i. c, towards the vascular canal whence they are 

 supplied with nutrient fluid. 



In the interstitial osseous substance between the Haversian 

 systems, when it is present in small quantity, the lacunae, few in 

 number, often not exceeding from i to 3, are less regular in 

 arrangement, paid have also a more rounded form. If the inter- 

 stitial substance is distinctly lamellated and in larger quantity, the 

 lacunae are more regularly disposed, with their surfaces parallel to 

 the lamellae. The canaliculi of these lacunae are also connected 

 with each other, and with those of neighbouring systems. Lastly, 

 in the outer and inner fundamental lamella, all the lacunae are 



