ITS MORPHOLOGICAL CHARACTERS. 13 



continuity, there are two different kinds of minute canals, one 

 being much smaller than the other, and both perforating the 

 true osseous substance. The larger of these sets of tubules, 

 which have an average diameter of O'Ol 005'" (Kolliker),* and are 

 known as the Haversian canals, or canaHculi medullares, form a 

 net work in the more compact osseous tissue, and open (1) exter- 

 nally on the outer surface of the bone, and (2) internally, on the 

 walls of the medullary cavities and spaces. The substance, how- 

 ever, which is surrounded by these spaces, is by no means to be 

 regarded as the matrix of bone as a perfectly continuous tissue, 

 for we find in it a third group of tubules by which the bone is 

 converted into a thoroughly porous substance. It is these tubules 

 which were formerly regarded as the special morphological elements 

 of osseous tissue, and were known as the bone-corpuscles and 

 ductuli chalecophori : they are empty spaces, which, on examining 

 dried sections of bone under the microscope by transmitted light, 

 are such conspicuous objects from their black colour, or rather 

 their opacity. These elongated lenticular bone-cavities, which 

 have, according to Kolliker,t an average length, breadth, and 

 thickness of O'Ol'", 0'004"', and 0*003'" respectively, send out innu- 

 merable intercommunicating off-shoots (the above-mentioned duc- 

 tuli chalecophori), and convert the matrix of the bones into a most 

 porous material. 



All these cavities, which we find in macerated and dried bones, 

 are filled in fresh bones with various tissues and materials which 

 do not pertain to the osseous matrix the true object of chemical 

 examination. It is well known that the large cylindrical cavities of 

 the tubular bones are filled with marrow, of which we shall speak 

 presently; this marrow is also found in the cancelli of the 

 apophyses of the cylindrical bones, and in the cavities of the 

 spongy substance of the flat and short bones, but is not contained 

 in the dense cortical substance ; hence it does not penetrate into 

 the Haversian canals, which only exist there. While the marrow 

 consists of a little connective tissue, and some vessels inter- 

 mingled with the true medullary matter, the Haversian canals 

 contain only blood-vessels and the nerves pertaining to them. 



With regard to the bone-corpuscles and their prolongations, it 

 was held, until very recently, that, as their name indicated, they 

 consisted essentially of calcareous salts, or, at all events, were 

 filled with them. This error, which was first exposed by Bruns 



* Mikrosk. Anat. Bd. 2, S. 278. 

 t Ibid. Vol. 2, p. 291. 



