576 THE MICROSCOPE. 



arises the transparent white line which often may be 

 noticed as surrounding each concentric system of laminse 

 and bone-cells : in some cases, however, part of the bone- 

 cells of the external row anastomose with another series 

 of bone- cells, which are situated between the concentric 

 laminee. The average length of the lacunae, or bone- 

 cells, in the human subject, is the l-2000th of an inch ; 



they are of an oval figure, 

 and somewhat flattened on 

 their opposite surfaces, and are 

 usually about one- third greater 

 in thickness than they are in 

 breadth ; hence, as will be 

 presently shown, it will become 

 necessary to know in what 

 direction a specimen is cut, in 

 order to judge of their compa- 

 rative size. The older anato- 

 mists supposed them, from their 

 opacity, to be little solid masses 

 of bone; but if the section be 

 treated with spirits of turpen- 



g. 319. A horizontal section of the tine coloured with alkanet- 

 AtfSL.**"** or ? '* ^ been soaked 



bone-cells arranged in parallel lines, m Very liquid Canada balsam 

 There are no Haversian canals pre- P . i rt ,~~4.'u ^c -H^ 14- 



sent; and when this specimen is ft any great length of time, it 



contrasted with that of fig. 317, can then be Unequivocally de- 

 it will be noticed that the canali- , , A , ,, ^ u 



cuii given off from each of the monstrateo. that Dotn tnese 

 rnuS^ncoSptuoTSthal ^stances will gain entrance 

 of the reptile. into the bone-cells through 



the canaliculi. The bone-cells, when viewed by trans- 

 mitted light, for the most part appear perfectly opaque ; 

 and they will appear the more opaque the nearer the section 

 of them approaches to a transverse one : for when the cells 

 are cut through their short diameter, they are often of such 

 a depth that the rays of light interfere with each other in 

 their passage through them, and darkness results; whereas, 

 if the section be made in the long diameter of the cells, 

 they will appear transparent. When viewed as an opaque 

 object, with a dark ground at the back and condensed 

 light, the bone-cells and canaliculi will appear quite white, 



