TISSUES OF THE BODY. 



239 



d 



secondarily from metamorphosed descendants of cartilage or connective- 

 tissue cells, and may therefore be regarded as the most complex 

 structure of this group. It consists of a network of stellate ramifying 

 spaces containing cells, and an abundant intermediate substance of homo- 

 geneous nature. The latter is remarkable for its extreme hardness and 

 solidity, and renders the whole the most resistent of all the more widely 

 spread tissues. Its specific gravity in the compact substance of hollow 

 bones is 1-930; in the spongy, 1-243 (Krause and Fischer). As the 

 name expresses, the occurrence of this tissue is in the human body normally 

 confined to the bones, if 

 we except a thin coating 

 on the roots of the teeth. 

 Its distribution, however, 

 among the vertebrates, pre- 

 sents considerable variety. 



As is well known, bones 

 are divided by anatomists 

 according to their form, 

 into the long or cylin- 

 drical, the flat or tabular, 

 the short or irregular. 

 Again, in accordance with 

 their texture, into the 

 compact (in which the 

 tissue has the appearance 

 of a solid continuous 

 mass), and the spongy or 

 cancellated, in which the 

 osseous substance, occur- 

 ring in the form of bands 

 and plates, encloses a sys- 

 tem of cellular intercom- 

 municating cavities. The 

 cylindrical bones display 

 a compact texture, except 

 in their terminal portions 

 or epiphyses, whilst those 

 belonging to the short or 

 irregular class are formed 

 of spongy tissue, with the 

 exception of their super- 

 ficial layers. In tabular 

 bones we encounter 

 spongy substance or dip- 

 Ibe clothed externally by 

 laminse of a very hard 

 tissue known as vitreous 

 layers (Glastafeln). 



The great hardness of osseous tissue does not admit of the usual 

 methods of examination being applied to it, and we are obliged either to 

 have resource to plates which have been sawed out and ground thin, or 

 we must extract from the tissue its solid mineral constituents, after which 

 the decalcified remainder (bone-cartilage, as it has been inappropriately 



f 



Fig. 232. Perpendicular section through a human phalanx. 

 At a and 6, two medullary canals with branches, c and d; , 

 the orifices of canaliculi appearing as dots; /, osseous cells 

 filled with air. 



