THE OSSEOUS SYSTEM. 279 



blance to certain sections of teeth (Fig. 117). The canaliculi of these 

 lainellsB communicate, in part as usual with each other, in part open on 

 the external and internal surfaces of the bone (Pig- 118). At the points 

 of insertion of tendons and ligaments 



. Fi"-. 118. 



into the bones, the canaliculi of the ^.. ^ . i^t^ . aM s^:^^^^.^,^'^^^^.^.-..^. . , ^ ,1,.-., ^ -^ 



outermost lacuna) probably terminate i0-;^^ii^:^::-::y-:-lj-^^^^ 



in blind extremities ; a condition which i^^[^!i^i-}^^^!j::^i'^^i^'-^'^ 



obtains in every case, in those parts fe^i-V^^^ii^^i^/;;:" ^^•:-^^^^^ 



of bones which are covered with car- ^■';>>:V:':";v^''^"^ 



tihige (articular ends, ribs, surfaces of ^'/^//•-■y^^'irp'.'':''-''-^''::.:^- 



the bodies of the vertebra?, (fee.) In V?"^-- ';.:V 



the rods, fibres, and plates of the \.';i'. ;■■;.:: -'v^ 



spongy substance, the lacunar are dis- " '^ - •■-. 



posed 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 anastomose also, in these situa- 

 tions, by means of their canaliculi ; and the most superficial lacuniTS 

 open freely into the cancelli. 



The size and shape of the lacuna?, in man, upon the whole, vary but 

 little. By far the greater number are melon-seed-shaped or lenticul;^ 

 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 0-01-0'014 of a line, frequently under and above that size, 

 or from 0*006 to 0-0 IG, rarely 0-02 or even 0-024 of a line (cranial 

 bones, lower jaw). The breadth, measured in horizontal sections, is 

 0-003-0'006 of a line; in transverse, it is usually somewhat greater, or 

 as much as 0*008, or even 0*01 of a line, because the limits between the 

 canaliculi and lacuna; cannot always be accurately defined. Their thick- 

 ness or depth, lastly, in the smallest lacuniB, is 0*003-0*001, and in the 

 larger 0-002-0-001 of a line. The diameter of the spherical lacunae is 

 0*000-0*008 of a line. The canaliculi are, on the average, 0*008-0*016 

 of a line long, seldom less or more, up to 0*02 and 0*024 of a line; in 

 diameter they measure 0*0004 of a line; at the finest extremities, 0*0005- 

 0-0008, on the average; 0*0008-0*001 of a line, at their origin from the 

 lacuna?. Their true distance apart, in horizontal sections, in which they 

 appear as holes, is 0*0008-0*002 of a line; in transverse sections, in 

 which they produce the radiating stria?, in consequence of their being 

 viewed in several planes, they appear to be somewhat closer together, or 

 at distances varying from 0*0008-0*0012 of a line. The circumference 



Fio. 118. — Portion of the surface of the tibia of the calf, viewed on the externa! aspect, 

 magnified 350 diam. : the numerous points are the openings of the canalicuH ; the dark, 

 larger, indistinct spots indicate the lacunEe to which these canaliculi belong, appearing from 

 a greater depth. 



