72 CONNECTIVE TISSUES BONE. 



canals present themselves at intervals, sometimes connected by a transverse 

 canal where the section happens to traverse this. Around these orifices the 

 osseous matter is arranged m the form of cylindrical lamellse, producing the 

 appearance of concentric circles, the number varying from five to twenty 

 for each Haversian canal. Each lamella presents a clearer internal and a 

 darker external part. lu the clearer portion of the lamella, or in the 

 spaces intervening between the lamellae, numerous lacunre are situated, the 

 canaliculi from which penetrate the adjoining lamellae, producing, as Dr. 

 Sharpey 1 has stated, the same appearance as would be seen on boring holes 

 to some depth in a straight or crooked direction through, the leaves of a 

 book, excepting only that the passages have proper parietes. On minute 

 examination of bones softened in acid, the lamellae are found to present a 

 well-marked fibrous structure, the fibres being transparent and decussating 

 with each other to form an extremely fine network, and those lamellae that 

 are formed by the periosteum as well as the outer lamellre of the Haversiau 

 system are often connected or bolted together by perforating bundles of fibres 

 of white fibrous or of yellow elastic tissue. The spongy flat bones contain 

 from 12 to 30 per cent, of water, the compact tissue from 3 to 7 per cent. 

 The chemical analysis of dried bone shows that it consists of from 30 to 34 

 per cent, of animal matter, which, on boiling yields gelatin, and from 66 to 

 70 per cent, of mineral matter, of which about 57 parts are composed of 

 calcium phosphate, 8 parts of calcium carbonate, 1 part of calcium fluoride, 

 and 1 part of magnesium phosphate. 2 The degree of hardness of bones 

 does not altogether depend, as shown by the experiments of Dr. Stark, 3 on 

 the proportion of mineral deposit they may contain ; for the flexible, semi- 

 transparent, easily-divided bones of fish contain as large a proportion of 

 earthy matter as the ivory-like leg bones of the deer or sheep. As a general 

 rule, the bones of the extremities contain more calcium carbonate and phos- 

 phate than those of the trunk, and the larger long bones more than the 

 smaller ones. 4 There is no difference in the Composition of the correspond- 

 ing bones of the two sides of the body, 5 and within certain limits (20 80) 

 age has little or no influence upon it. It is also but very slightly influenced 

 either by the proportion or the nature of the salts centaiued in the food. 6 

 The power of resisting pressure possessed by bone is very great, being nearly 

 three time's more than elm or ash, and twice as much as box, yew, or oak. 7 

 The weight of the skeleton is to that of the whole body about as 10.5: 100 

 in man, and as 8.5 : 100 in woman. The specific gravity of bone varies 

 from 1.898 to 1.964. The natural process of absorption which parts of vari- 

 ous bones and the fangs of the first set of teeth undergo is effected by means 

 of many nucleated cells, to which Kolliker 8 has recently applied the term 

 of osteoclasts or osteophagous cells. These present a close brush of hairs on 

 that part of the cell which is turned towards the bone undergoing absorp- 

 tion, and it is by their action that all foramina, canals, and grooves in bone 

 are produced. In the long bones of Man and of most Mammalia, the central 



1 Introdiicliiin to Quain's Anatomy, 7th edition, p 96. 



2 For further details, and for tin- percentage composition of the Ashes of Bones and 

 Teeth, sco Aeby, Centralhlatt, 1871, p. 5(11 ' 1873, p. 97. 



3 Edinburgh Medical and Surgical Journal, April, 1845. 



4 Fossil bones sometimes contain a very large amount of Calcium fluoride. Lns- 

 saigne, for example, found 15 per cent, in a tootli of the Anoplotlierium. 



* Aeby, Centralblatt, 1871, p. 5(il. 



6 See Weiske'a Zeits. f. Biologie, Band vii, pp. 179 and 333, viii, 239, and ix, 541 ; 

 and 1'apillon, Rubin's Journal do 1'Anat., t. vi, 153. Hcitzmann (Wien. An/.eig., 

 1ST-!, p. 113) shows that either feeding with, or subcutaneous injection of lactic acid 

 produces Rachitis and Osteomalacm in Carnivora. 



7 Robinson, in Lancet, 184f>, vol. i, p. 340. 



8 Verhandlung der Wur/burger I'hysik und Gcscllschuft, N. F., Band ii, 1872. 



