1 08 LOCOMOTION. [CHAP. v. 



great medullary canal itself, are likewise involutions of the osseous 

 surface, though for a partly different end. These larger and more 

 irregular cavities in bone may be considered as a dilated form of 

 Haversian canals. They contain vessels not only for the nutrition 

 of the thin osseous material forming their walls, but also for the 

 supply of the fat enclosed within them. 



Thus the true osseous substance may be described as lying in 

 the interstices of a vascular membrane, or of a network of blood- 

 vessels. The most interesting points in the minute anatomy of 

 bone relate to the mode in which nutrition is provided for in those 

 parts not in immediate contact with the blood-vessels. We have 

 already seen that considerable masses of cartilage derive their nu- 

 triment from vessels placed on their exterior only, apparently by a 

 kind of imbibition, perhaps aided by the presence of the nucleated 

 cells, and by a more or less fibrous texture : but bone, which is of a 

 far harder and denser nature, is unable to imbibe its nourishment 

 so easily. Hence its surface is greatly augmented by the arrange- 

 ments already detailed; and, in addition to this, the osseous tissue 

 itself is provided with a special system of microscopic cavities and 

 canaliculi, or pores, by which its recesses may be irrigated, to a 

 degree of minuteness greatly exceeding what could have been ef- 

 fected by blood-vessels alone, consistently with the compactness and 

 density required in the tissue. The study of this delicate appa- 

 ratus will now demand attention ; but a few words must be pre- 

 mised on the ultimate structure of the osseous tissue. 



It appears from the researches of Mr. Tomes, about to be pub- 

 lished in the Cyclopaedia of Anatomy, that the ultimate structure of 

 the osseous tissue is yranular. The granules of bone are often very 

 distinctly visible, without any artificial preparation, in the substance 

 of the delicate spiculoe of the cancelli, viewed with a high power, 

 and in various sections of all forms of bone. They may be gene- 

 Fi 21 rally obtained in calcined bone, either by bruising 



a fragment of it, or by steeping it in dilute muri- 

 atic acid; they may also be made very evident by 

 prolonged boiling in a Papin's digester. Those 

 represented in fig. 21 were obtained in the latter 

 mode. The granules vary in size from --- 5- to 3-4 QQT 

 of an inch. In shape they are oval or oblong, 

 bone! in Js a oi e atS ai m!d 8 [ and often angular. They cohere firmly together, 



possibly by the medium of some second substance. 

 In some few instances, Mr. Tomes has met with 

 a very minute network, which seems adapted to receive them in 



