62 



SIXTH LECTURE. 



Fig. 60. — Lacunas (</, a) with their 

 numerous offshoots, opening into the 

 transversely divided Haversian canal 

 {V- 



produced by two human hands when their volar surfaces rest 

 over each other. The length is 0. 1805 to 0.0541, the breadth 



O.0068 to 0.0135, tne thickness 

 0.0045 to 0.009 mm. The offshoots 

 of this system of cavities, very nar- 

 row canals of O.OO14 to 0.0018 mm. 

 diameter, permeate the entire tissue 

 in innumerable multitudes, ramifying 

 irregularly in a radial direction. 

 They open (1) in the Haversian 

 canals {b), (2) on the surface of the 

 bone, and (3) in the large medullary 

 cavity in the interior. Transverse 

 and longitudinal sections (the tan- 

 gential must also be added) teach 

 this most distinctly. 

 In the dried bone, the marvellously complicated system of 

 canaliculi has become filled with air in a condition of the 

 finest division. An earlier epoch erroneously assumed the 

 contents to be inorganic hardening material, to be the finest 

 molecules of the so-called bone earths. Hence the name of the 

 " calcareous canaliculi." If we place the small thin plate in 

 turpentine oil, the thousands upon thousands of finest canali- 

 culi rapidly fill with the fluid through capillary attraction. 

 The bone corpuscle now presents the appearance of a cavity; 

 the fine canaliculi disappear more or less in the basis sub- 

 ^=^ stance. 



But what does this remarkable canal work 

 contain during life ? 



We answer to this, there is in the lacunae a 

 protoplasmatic membraneless cell (Fig. 61, b). 

 Whether this bone cell, the equivalent of the 

 connective-tissue corpuscle, sends off capillary 

 offshoots into the lacunae, which is very prob- 

 able, we do not yet know. The latter canalic- 

 ular system is certainly filled with transuded blood plasma. 

 This fluid must, besides, be rather stagnant, for the frictional 



Fig. 61. — From 

 the fresh ethmoid 

 bone of the mouse; 

 a. basis substance; 

 t, the bone cell. 



