THE OSSEOUS SYSTEM. 



379 



as the enlargement of the sinuses in the cranial bones, of the 

 points of insertion of muscles and ligaments, and of the vascular 



described; but this investment was nothing but the clear, often homogeneous, 

 calcareous matter, gradually encroaching on the matrix and inclosing the cor- 

 puscles. 



We consider, then, that the process of ossification in primary and secondary bone 

 is identical; the deposition 

 of the calcareous matter in 

 granules or as a homogeneous 

 infiltration, being of no con- 

 stancy or importance. In 

 each case the deposit takes 

 place in the matrix, and leaves 

 spaces (lacunae) round the 

 corpuscles (nuclei, granular 

 cells). Subsequently, the 



canaliculi are developed in 



the matrix by a process of 



resorption ; while their walls 



and those of the lacunae may 



or may not become chemically 



differentiated from it. At 



the same time, the matrix 



may or may not break up 



into lamina? and "osteal cells" 



or granules. Its variability 



in this respect is neither 



more nor less remarkable 



than the greater or less fibril- 

 lation of the corresponding 



element of connective tissue, 



or than the inconstancy of 



the disposition of the cleavage 



lines of the same element in 



striped muscle. 



As little is any line of demarcation to be drawn between primary and secondary 



bone as regards the tissues from which they proceed. Indifferent tissue, in 



which calcareous matter is deposited at once, is the basis of secondary bone ; 



an identical tissue — in which to serve a temporary purpose chondrin is deposited, 



being subsequently withdrawn and replaced by calcareous salts — is the basis of 



45 



V-.. 



2. 



Fig. 136 A. 1, wall of Haversian canal from the metatarsal bone of a Calf; a, 

 structureless matrix ; b, homogeneous calcareous deposit replacing it and forming 

 the inner lamina of the canal; c, more external lamina broken up into "osteal cells;" 

 d, corpuscles; e, lacunae : 2, ossifying cartilage of the Skate, for comparison ; letters 

 as above. Both x 600. 



