THE OSSEOUS SYSTEM. 305 



teeth (fig. 117). The canaliculi of these lamellae communicate, 

 in part as usual with each other, in part open on the ex- 

 ternal and internal surfaces of the bone (fig. 118). At the 

 points of insertion of tendons 



and ligaments into the bones, Flg " 118- 



the canaliculi of the outer- PlfpP?p?|Pj$|i^ 

 most lacunae probably ter- 

 minate in blind extremities ; 

 a condition which obtains 

 in every case, in those parts 

 of bones which are covered 

 with cartilage (articular ends, 



ribs, surfaces of the bodies "-,.-.- ' 'L '■"-• ■'_'-'■. -'".V-' : - -^j^-j 



of the vertebrae, &c.) In the 



rods, fibres, and plates of the spongy substance, the lacunae are 

 disposed in every possible direction, but, for the most part, with 

 their long axis parallel to that of the fibres, bars, &c, and with 

 their flat surfaces directed towards the cancelli. They anasto- 

 mose also, in these situations, by means of their canalieuli ; 

 and the most superficial lacunae open freely into the cancelli. 



[The size and shape of the lacunae, in man, upon the whole, 

 vary but little. By far the greater number are melon-seed 

 shaped or lenticular, some, more fusiform or spherical. In 

 sections of bone well filled with air, in which alone I have made 

 my measurements, I find their average length to be 0*0] — 

 0014'", frequently under and above that size, or from O006 

 to 001 6'", rarely 002 or even 0-024'" (cranial bones, lower 

 jaw). The breadth, measured in horizontal sections, is 0-003 — 

 0-006'"; in transverse, it is usually somewhat greater, or as 

 much as 0-008'", or even 0-01'", because the limits between the 

 canaliculi and lacunae cannot always be accurately defined. 

 Their thickness or depth, lastly, in the smallest lacunae, is 

 0-003 — 0-004'", and in the larger 0002 — 0-004'". The 

 diameter of the spherical lacunae is 0-006 — 0-008'". The 

 canaliculi are, on the average, 0-008 — 0-016'" long, seldom less 



Fig. 118. Portion of the surface of the tibia of the calf viewed on the external 

 aspect, x 350 diam. The numerous points are the openings of the canaliculi ; the 

 dark, larger, indistinct spots indicate the lacunae to which these canaliculi belong, 

 appearing from a greater depth. 



i. 20 



