301 SPECIAL HISTOLOGY. 



the canaliculi arising from the inner aspect of the innermost 

 lacunae of an Haversian system, proceed towards the canal, with 

 which they, by this means, communicate, as may be clearly seen 

 in thin, perpendicular, and transverse sections of bones filled 

 with air, and in the walls of medullary canals laid open 

 longitudinally. From the borders and external aspect of the 

 same lacunae other canaliculi are given off, which perhaps 

 occasionallv terminate in blind extremities, but for the most 

 part communicate Avith those of the neighbouring, and particu- 

 larly of the outer lacunas. The succeeding rows of lacunae are 

 all mutually connected in a similar way, and thus the network 

 of canaliculi and lacunae extends to the outermost lamellae of 

 the system, where the lacunae either communicate with those 

 of the contiguous systems or of the interstitial lamellae, or 

 terminate independently, in which latter case (fig. 115^) all 

 the canaliculi, or at least most, and the longest of them, 

 proceed inwards, that is to say, towards the vascular canal, 

 from which they derive their nutritive fluid. 



In the interstitial osseous substance between the Haversian 

 systems, when it exists in small quantity, the few lacunae, 

 frequently not more than from 1 to 3 in number, are disposed 

 more irregularly, and also present a rounded form (fig. 115 e); 

 when the interstitial substance is more abundant, and distinctly 

 lamellar, the lacunae are also disposed more regularly, with 

 their sides parallel to those of the lamellae. The canaliculi 

 of these lacunae, in like manner, communicate with each other, 

 and with those of the neighbouring systems. In the outer and 

 inner fundamental lamellae, lastly, the lacunae are all placed 

 with their surfaces parallel with those of the lamellae, and con- 

 sequently looking, for the most part, inwards and outwards, or 

 towards the centre and periphery of the bone. In transverse 

 sections they precisely resemble those of the Haversian systems, 

 only that they are but little or not at all curved, except in the 

 smallest cylindrical bones. In longitudinal sections, whether 

 perpendicular or parallel to the surface, they present the con- 

 ditions above described, with this limitation, however, that a 

 larger number of lacunae, of course, are seen in the same space 

 in the latter case than in the former, and also that the sieve- 

 like aspect described above is more frequently observed, giving 

 the bone considerable resemblance to certain sections of 



