224 STRUCTURE OF BONE. 



become separated farther and farther from one another. 

 (PI. VII, fig. i.) The appearances of a cell-wall around 

 the bioplasm in the fully-formed tissue, and other alterations 

 which occur, and anomalous appearances which often result 

 as age advances, can be even more readily understood upon 

 the view here advanced, than upon the intercellular-sub- 

 stance theory, which has been so strongly advocated by 

 some observers. See the figures in PI. VII. 



Bone. In its formation this tissue passes through two 

 stages : i. The organic matrix is formed by bioplasm ; and, 

 2. The matrix is subsequently converted into bone. In bone 

 formation the matrix of cartilage (PI. VI, fig. 3,) or of a 

 form of fibrous tissue is calcified by the precipitation in its 

 substance of calcareous matter, the deposition of which 

 commences at a point midway between contiguous bioplasts. 

 The bioplast is at length encroached upon by the calcareous 

 matter, and is at last enclosed in a small space or lacuna, 

 which communicates with adjacent lacunae by channels 

 which have been left free from the first. Through these, 

 nutrient pabulum has flowed towards the living bioplasts 

 during the deposition of the calcareous matter. 



The formation of the permanent bone of the greater 

 part of the skeleton of vertebrate animals is, however, a 

 complex process, for a description of which see " The 

 Physiological Anatomy and Physiology of Man," Part II, 

 or my work on Bioplasm, Lecture VIII, p. 141. Some 

 idea of the changes which occur may however, be formed 

 if fig. i, PL VIII, be attentively examined. This is an 

 accurate copy of a section through the periosteum and 

 bone-tissue of the femur of a kitten, and was taken from a 

 well-prepared specimen, which showed all the points very 

 clearly. 



