CONNECTIVE TISSUES BONE. 



73 



FIG. 34. 



cavity, which may be considered as an enlarged Haversian canal, is filled 

 with the fatty matter known as marrow. This substance differs from ordinary 

 adipose tissue in the nearly complete absence of connective tissue, the cells 

 being supported by the spiculn) and lainellre of bone which project into the 

 cavity of the shaft. It is composed of 96 parts of fat, 3 parts of fluid, and 

 1 part of connective tissue. In the cancellous tissue forming the expanded 

 extremities of the bones, a peculiar reddish fluid is found, to which the term 

 marrow has also, though incorrectly, been applied, since it contains only a 

 trace of fat. Its percentage composition is : Water, 75 parts ; albumen, 

 fibrin, and salts, 25 parts. Bones are but feebly supplied with sensibility. 

 A few small nerves may, however, be seen to enter the shafts of the long 

 bones with their nutritious arteries, and to be distributed in the eudosteum. 

 50. The development of Bone 1 consists in the conversion either of fibrous 

 membrane, or of cartilage into osseous tissue. In the former case the ossi- 

 fication is said to be intramembranous, in the latter, iutracartilaginous. 

 The intramembranous form of ossification principally occurs in the flat bones 

 of the head, and is also the mode by which the long bones increase in girth. 

 The primary tissue presents the appearance of ordinary fibrous membrane, 

 in the meshes of which are numerous nuclei, os- 

 teoblasts, or corpuscles of " germinal matter." 

 In the process of ossification, the fibres become 

 the seat of calcareous deposit, which radiates out 

 from a central point, advancing along the fibres, 

 and rendering them opaque and granular. By 

 the development of connecting spiculse between 

 the first-formed radiating strise, irregular areolse 

 are soon produced, in many parts partially or 

 wholly inclosing bloodvessels. The bone then 

 increases, in thickness, by the deposition of new 

 bone proceeding either from the calcification of 

 successive generations of osteoblasts, which line 

 the areola3 like an epithelial layer, or of a ma- 

 terial excreted by and external to the osteoblasts ; 

 and in extent, by the lateral development of the 

 radiating striae. In intracartUaginous ossifica- 

 tion certain preparatory changes occur in the car- 

 tilage, which consist in its becoming vascular, 

 and in its cells undergoing repeated division, so 

 as to form cylindrical piles or columns, separated 

 from each other by intercellular substance (Fig. 

 34). It is in this substance that the ossific matter 

 is first deposited, appearing in the form of dark 

 granular spiculte, which shoot up between the 

 rows of cells from the surface of the subjacent 

 bone, or radiate from a central point. If the 

 cartilaginous and the osseous substance be sepa- 

 rated at this period, the ends of the rows of car- 

 tilage-cells will be found to be received into deep 

 narrow cups of bone; and the nuclei in immediate contact with the ossi- 



Cartilage at the seat of Ossifica- 

 tion, showing at its lower portion 

 the clusters of cells arranged in 

 columns, each of which is inclosed 

 in a sheath of calcified intercellu- 

 lar substance. 



1 For good papers on the development of Bone see C. Kutschin in Rollett's Un- 

 tersuch. aus dem Instit. fur Phys. and Histologie in Graz, 1870 ; Kolliker, Die nor- 

 malem Resorption des Knochengewebe, Leipzig, 1873; Wolff, Klin. Wochenschrift, 

 1863, No 6; Oilier, Brown-Seqmird's Archives de Physiologic, 1873 ; Wogner in 

 Virchow's Archiv, 1874, Band Ixi, p. 44; Strelzoff, Ce'ntralblatt, 1872, p. 4*49, and 

 1873, p. 273. 



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