BONE. cvii 



la a long boiie these precursory vessels are seen at either end of the ossified 

 portion of the shaft, forming a red zone in that part of the cartilage ID to 

 which the ossification is advancing. The vessels are lodged in excavations 

 or 1 ranching canals in the cartilage, (fig. LI. a,) which also contains granular 

 corpuscles and soft matter. Other vascular canals enter the cartilage from. 

 its outer surface, and conduct vessels into it directly from, the perichondrium; 

 at least, this may be seen when the ossification approaches near to the ends 

 of the bones. 



Dr. Baly has observed that in a transverse section of the ossifying cartilage, its 

 cells appear arranged in radiating lines round the sections of the vascular canals ; * 

 and I may also remark that in many of these radiating groups the cells successively 

 diminish in size towards the centre, that is, as they approach the canal. The canals 

 which enter from the surface of the cartilage are probably formed by processes from 

 the vascular subperichondrial tissue, which, excavating the canals by absorption, 

 thus extend themselves through the mass of cartilage; and as the perichondrium 

 affords material for the growth of the cartilage at the surface, so these vascular pro- 

 cesses probably yield matter for the multiplication of the cells in the interior of the 

 mass. The canals which pass into the cartilage from the ossified part are, in like 

 manner, most probably formed by processes of the subperiosteal tissue which pierce 

 the bone and extend through the medullary cavities within it to the cartilage, into 

 which they penetrate for a short way beyond the advancing limit of ossification. 



To examine the process more minutely, let an ossifying bone be divided 

 lengthwise, as in fig. LI. , and then from the surface of the section (as at a, 6) 

 take off a thin slice of cartilage, including a very little of the ossified 

 part, and examine it with the microscope. Such a view, seen with a 

 low power, is shown in fig. LII. The cartilage at a distance from the sur- 

 face of the ossified part has its cells uniformly disseminated in the matrix, 

 (as at a, where it appears in the figure as if granular,) but at and near to the 

 limit where the ossification is encroaching upon it, the cells are gathered into 

 rows or oblong groups, between which the transparent matrix appears in form 

 of clear longitudinal lines (often obscurely striated) obliquely intersecting each 

 other (6). Tomes and De Morgan state that these rows are formed by 

 segmentation of the cartilage-cells transversely to the line of ossi6c advance. 

 Turning now to the newly formed bone (c), which from its dark opaque 

 aspect contrasts strongly with the cartilage, and tracing it towards their 

 mutual boundary, we see plainly the dark lines of ossification shooting up 

 into the clear spaces of the cartilage between the groups of corpuscles. The 

 earthy deposit, in fact, proceeds through the matrix, and affects also those 

 parts of the cartilage-capsules which form the circumference of a group, so 

 that the new osseous substance forms in the first instance oblong areolse or 

 loculi, which inclose the groups of cells. This is further illustrated by a 

 thin transverse section, carried nearly parallel to the ossifying surface, and 

 partly encroaching on it, so as to take off a little of the bone along with 

 the cartilage, as represented in fig. LIII. In this view we see, at one part, 

 the dark and nearly circular sections of the newly formed osseous areolae ; 

 at another, sections of the rows of cartilage- cells with the clear matrix 

 between and around them, and into this the dark ossification is advancing. 



On using a higher power, as in figs. LIV. and LV., it will be seen that the cells 

 forming the groups are placed with their long diameter transversely, as if they had 

 been flattened and piled upon one another ; but in the immediate vicinity of the bone 

 they become greatly enlarged and more rounded. In most of them the outline 

 of the capsule is distinct from that of the mass within. As to the matter they 



* Muller's Physiology, plate I., fig. 16. 



