THE OSSEOUS SYSTEM. 279 



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

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

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

 of insertion of tendons and ligaments 

 into the bones, the canaliculi of the 

 outermost lacunas probably terminate 

 in blind extremities ; a condition which 

 obtains in every case, in those parts 

 of bones which are covered with car- 

 tilage (articular ends, ribs, surfaces of 

 the bodies of the vertebrae, &c.) In 

 the rods, fibres, and plates of the 

 spongy substance, the lacuna? 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 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*01 - 014 of a line, frequently under and above that size, 

 or from 0-000 to 0-016, 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 O'Ol of a line, because the limits between the 

 canaliculi and lacunae cannot always be accurately defined. Their thick- 

 ness or depth, lastly, in the smallest lacunae, is 0-003-0-004, and in the 

 larger 0-002-0-004 of a line. The diameter of the spherical lacunae is 

 0-006-0-008 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 

 lacunae. 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 striae, 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 



FIG. 118. Portion of the surface of the tibia of the calf, viewed on the external aspect, , 

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

 largor, indistinct spots indicate the lacunae to which these canaliculi belong, appearing from 

 a greater depth. 



