BONE. 



Fig. 06. 



fibrous membrane or perichondrium, the future periosteum, Vessels 

 ramify in this membrane, but none are seen in the cartilage until ossi- 

 fication is about to begin. 



In a long bone the ossification commences in the middle and proceeds 

 toward the ends, which remain long cartilaginous, as represented in 

 fig. 56. At length separate points of ossification appear in them, and 

 form epiphj-ses, which at last are joined to the body of the bone. 



The newly formed osseous tissue is red and ob- 

 viously vascular, and blood-vessels extend a little 

 way beyond it into the adjoining part of the carti- 

 lage. In a long bone these precursory vessels are 

 seen at either end of the ossified portion of the 

 shaft, forming a red zone in that part of the carti- 

 lage into which the ossification is advancing. The 

 vessels are lodged in excavations or brauching canals 

 in the cartilage, (fig. 56, a) which also contains 

 granular corpuscles (osteoblasts). Other vascular 

 canals enter the cartilage from its outer surface, 

 and conduct vessels into it directly from the peri- 

 chondrium ; at least, this may be seen wlien the 

 ossification approaches near to the ends of the 

 bones. 



Baly 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 it may 

 also be here remarked that in many of these radiating 

 groups the cells successively diminish in size towards the 

 centre, that is. as they aiaproach the canal. The canals 

 Avhich enter from the surface of the cartilage are i^robablj' 

 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 perichondriiim affords material for the growth of the 

 cartilage at the sui'face. so these vascular processes probalily 

 yield matter for the multiiilication of the cells in the 

 interior of the mass. The canals which pass into the carti- 

 lage from the ossified part are. in like manner, most pro- 

 liably 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. 



Fig. 56. — Humerus 

 OF A F<ETUs, Na- 

 tural SIZE. 



The uiiper half is 

 divided longitudin- 

 ally, a, cartilage, h, 

 lione, ■which termin- 

 ates towards the car- 

 tilage by a slightly 

 convex surface. 



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

 divided lengthwise, as in fig. 56, and then from the surfoce of the sec- 

 tion (as at a, h) 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. 57. The cartilage at a distance 

 from the surface 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 ol)long groups, between which the 

 transparent matrix a])pears in form of clear longitudinal lines (often 

 obscurely striated) obliquely intersecting each other {h). Turning now 



* :\luller"s Physiology, plate I., fig. 16. 



