70 CONNECTIVE TISSUES BONE. 



cent, of fresh cartilage, and the inorganic substances, of which the sulphates 

 of potash and soda constitute the major part, do not amount to more than 

 2.5 per cent. (Hoppe-Seyler.) Permanent cartilage is employed in the con- 

 struction of the body chiefly on account of its resiliency, and on account of 

 the extremely smooth surface which it presents, permitting free movement 

 in the joints, where it is lubricated by the albuminous synovial fluid, with 

 the least possible amount of friction. 



48. BONE. The bones constitute the organs of support for the softer tis- 

 sues, and with the muscles form a system of levers by which locomotion, 

 prehension, mastication, and various other movements are effected. They 

 more or less perfectly inclose the cavities of the head, chest, and pelvis, and 

 by their hardness and elasticity constitute an efficient protection to the im- 

 portant organs therein contained. They are divided according to their form 

 into long, short, irregular, and flat bones. In the long bones the shaft is 

 pierced by a central canal, which runs continuously from one extremity to 

 the other, and the hollow cylinder which surrounds this is very compact in 

 its structure. On the other hand, the dilated ends of the bone are composed 

 of a spongy or cancellated structure, which is made up of osseous lamellre 

 and fibres interwoven together ; the arrangement of which has been shown 

 by H. Meyer 1 and Wolff 2 to be by no means irregular or fortuitous, but ex- 

 quisitely adapted for the mechanical functions they have to perform and in 

 exact accordance with theoretical requirements ; 3 a multitude of minute 

 chambers or cancelli freely communicating with one another and with the 

 cavity of the shaft are thus formed, whilst the w r hole is capped with a thin 

 layer of solid bone. In the flat bones of the head, and less distinctly in the 

 scapula and ilium, we find the two surfaces composed of solid osseous texture, 

 with more or less of cancellated tissue, called the diploe, interposed between 

 the layers. This, however, is sometimes deficient, leaving a cavity as in the 

 frontal sinuses. Finally, we frequently meet (especially in the ethmoid and 

 sphenoid bones) with thin lamellse of osseous substance, resembling those 

 which elsewhere form the boundaries of the cancelli. These consist of but 

 one layer of osseous substance, and are not penetrated by vessels, but are 

 nourished by those ramifying on their surfaces ; and they consequently ex- 

 hibit the elements of the osseous substance in their simplest form. It will 

 be desirable, therefore, to commence with the description of these. 



49. When a thin natural lamella of this kind is examined, it is found to 

 belong to the doubly refracting tissues, and to be chiefly composed of a sub- 

 stance which is nearly homogeneous, 



FlG - 31 - though sometimes exhibiting indistinct 



traces of a fibrous arrangement. In 

 the midst of this granular substance a 

 number of dark spots are to be seen, 

 presenting an oval form, and giving 

 off, from their sides and extremities, 

 rx numerous radiating prolongations of 

 extreme minuteness, and frequently of 



considerable length. The dark spots 

 Lacuna of Osseous S ubstan,e magnified 500 sm&u cavities termed l acHHa , un d 



diameters ; a, central cavity; 6, its raimnca- ' 



ti ons . the branched prolongations or can- 



/ii-u/l, are tubular channels, which, 



though far too small to convey blood-corpuscles, yet bring the fluid ele- 

 ments of the blood, or matters secreted from them, into close relation with 



Die Architectur der S|><niixiosu, Reiuhert and Dubois-Rnymond's Art-hiv, 1867. 



' 



Aivliiv, I5;ind 1, p. 389. 



3 On this point sec also (Julmann, Die graphite-he Shitilc. Zurich, 1806. 



