THE OSSEOUS SYSTEM. 275 



it affords, according to Tomes, minute angular granules, from -Jth to 

 the diameter of the human blood corpuscle, and measuring, according 

 to Todd and Bowman, gouoth-niosth of an inch, and which are also 

 rendered evident when bone is boiled in a Papins' digester. From these 

 particulars, and from the granular aspect of fresh bone, which has also 

 been noticed by Tomes and by Todd and Bowman, and moreover from 

 the pretty nearly equal size of the granules visible in it, with those 

 described by Tomes, and lastly, from the circumstance that bone treated 

 with hydrochloric acid, as well as when calcined, both present a perfectly 

 homogeneous substance without vacuities, it may be assumed that the 

 osseous tissue consists of an intimate mixture of inorganic and organic 

 compounds, in the form of closely connected minute granules. 



91. Bone Cavities or Cells, and Canaliculi (lacunce et canaliculi 

 ossium). In dried sections of bone, there are visible, scattered through- 

 out the entire osseous substance, in all the lamellae, microscopic melon- 

 seed-shaped corpuscles, with numerous, fine, ramified, and partially 

 anastomosing rays, whose opaque and white color (as viewed by direct 

 light) is due, not to the deposition of calcareous salts, as was formerly 

 supposed, and on which account they were termed " bone," or " calca- 

 reous corpuscles," but simply to their being filled with air. In fresh 

 bone, not yet deprived of its watery constituents, nothing can be seen 

 in these bone-cells or lacunae but clear contents with a nucleus, which 

 may best be described as the nutritive fluid of the bone, and conse- 

 quently the designation above given to these cavities is the most suitable. 



The lacunce are elliptical, flattened cavities, having an average length 

 of 0-01 of a line, 0-004 of a line wide, and 0-003 of a line thick, which 

 give off both from the borders, and particularly from the surfaces, a 

 great number of very fine canals, measuring 0-0005-0-0008 of a line in 

 diameter the bone canaliculi above-mentioned (Figs. 115, 116, and 117) 

 The lacunae are equally numerous in both of the lamellar systems before. 



tebrata, we have bone tissue without obvious granularity, and without obvious structure ; 

 and although it forms but a small part of the general mass, yet from its constant presence 

 at all ages and in all subjects, it must be regarded as an integral and normal part of mam- 

 marial bone. The granular condition of bone tissue is tolerably obvious in all preparations, 

 though it is much more marked in some specimens than in others. The amount of the 

 component granules varies in different parts of the same specimen, and in specimens taken 

 from different parts of the skeleton. Thus, in one situation, we may see laminae with a 

 highly transparent part gradually merging into a transparent tissue, while in another the 

 lamince may be granular throughout. Again, in young bone developed in cartilage, the part 

 between the cells becomes highly granular, fragments of which may be found in certain 

 adult bones, as in the petrous portion of the temporal bone. Bone near the articular surface 

 frequently presents a well-marked granularity." 



We may remark, in addition to this very just account of the minute structure of bone, that 

 of the lower vertebrata above referred to, the Skate offers one of the best examples of 

 structureless bone, in those polygonal plates which are developed (not on the surface, as is 

 commonly said, but) in the interior of the cartilaginous skeleton. TRS.] 



