81 GENERAL ANATOMY OF THE TISSUES. 



sometimes more homogeneous, sometimes finely granular, very 

 frequently lainellated, and hard and brittle from its being inti- 

 mately combined with calcareous salts ; the lacuna are for the 

 most part lenticular, and are united by very numerous fine pro- 

 cesses, the canaliculi ; by which some of them also open upon 

 the outer surface of the bones and into the larger and smaller 

 medullary and vascular spaces in the interior. The lacuna and 

 canaliculi contain a clear substance which may be regarded as 

 the nutritive fluid of the bones, and besides, a cell-nucleus ap- 

 pears in many cases, perhaps constantly, to be inclosed within the 

 lacunae. Besides these two most essential elements, which exist 

 in all bones, numerous vessels and nerves occur in most, as well 

 as, frequently, a peculiar substance, the medulla, which supports 

 them, and consists either of common fatty tissue, or of a loose, 

 scanty, connective tissue, with few fat cells and many peculiar, so- 

 called medulla-cells. These soft parts fill up the larger cavities in 

 the interior of thebones and in the spongy substance; but are to be 

 found also, at least partially, in narrowcanals which penetrate the 

 compact substance, the vascular or Haversian canals, which open 

 in all directions upon the outer and inner surfaces of the bones. 

 The matrix of the osseous tissue is composed of an intimate 

 combination of an organic substance, which perfectly agrees 

 with that of the connective tissue, and of inorganic compounds, 

 among which the phosphate and carbonate of lime are the prin- 

 cipal constituents. The fluid contained in the cavities and canals 

 is not thoroughly understood, but it probably presents a prepon- 

 derance of albumen, fat, and salts, like the serum. The bones, 

 from their solidity and inflexibility, serve as supports to the 

 „. or> softer organs or for their more secure in- 



Fig. 32. ° 



fjk £ closure ; and also perform special func- 



J-Vw \ t ions ; as, for example, the auditory ossicles 



■'' f(v;J '> ':'■' &■ ;ill| l the parts of the labyrinth which con- 



.','".- duct the sonorous vibrations. The de- 



■ t Q ?v . | velopment of the bones takes place in two 



w ' ,. C. V. r:.-' --' modes; firstly, by the metamorphosis of 



-** genuine cartilage, and secondly, by that 

 of a soft blastema composed of indifteient cells and of a fibrous 



Fig. 32. Six developing bone-cells from a rickety bone, as yet sharply defined 

 from the interstitial substance : a, simple bone-cells ; b, compound ones running to 

 a parent cell, with two secondary cells ; c, such arising from three cells, x 300. 



