(iKOWINCi HONE. 41 



not show clearly beyond their origins in the lacume. The 

 Haversian canals are incompletely filled by blood vessels, 

 around which are perivascnlar lymph spaces. The latter usually 

 contain some fat. 



The canaliculi open into the lymph spaces, their system 

 becoming thus continuous with that of the lymphatics. Other- 

 features recognised in the dry preparation, should be sought 

 for. 



Head of growing long bone. 1 V.8. Distal end of femur. Kitten 

 or rabbit, (p. 3, s. 22 & 24, c. P., ra. B.) (L) Observe the cartila- 

 ginous epiphysis (possibly with cancellous tissue in its interior), 

 find where it is implanted in the shaft, and note that the arrange- 

 ment of the cartilage corpuscles in the latter part, is in rows 

 parallel to the length of the bone. This is the lifting zone. 

 On its inner aspect, the substance of the epiphysis passes into 

 a network-like material, the primary cancellous tissue, which 

 diminishes in quantity the further into the shaft it is traced. 

 Examine (/7) the lifting zone. The outer longitudinal rows 

 of corpuscles form the zone of proliferation, deeper in, the 

 corpuscles increase in size, the intervening matrix is diminished 

 and has a faintly granular appearance, in the unsoftened 



ir rhe long bone is originally laid down as a cartilaginous rod. This rod is cut 

 across by the formation of the primary medullary cavity, thus yielding two cartilagi- 

 nous heads or epipliyses. These are implanted in the ends of the tubular shaft which 

 now becomes evident. The cartilaginous heads slowly recede in an axial direction 

 from the shaft by changes in the cartilage itself, and the shaft lengthens by groii't/i 

 at its ends, and thus keeps pace with the receding epiphyses. Later the cartilaginous 

 heads themselves become eroded and replaced by cancellous tissue which first gives 

 in them the appearance of the so-called centres of ossification. The lifting of the 

 heads occurs through the changes in the inner (sub-epiphysal) portion of the 

 cartilage, i.e., that portion which is embraced by the end of the shaft, and which 

 may therefore be called the lifting cartilage. Meanwhile, the shaft is increasing 

 in thickness by sub-periostial deposition, and it is maintained at a proportionate 

 thickness by the resorption of material from its inner surface. All bone formation is 

 due to osteoblasts and resorption to osteoclasts, both of which are corpuscular 

 constituents of the periosteum, or of its continuation inside the medullary cavity, 

 the Endosteum. All bones prefigured in cartilage, whatever their shape, undergo 

 similar changes, modified to suit their particular case. Bones not or only partially 

 preceded by cartilage are developed from periosteum, i.e., cranial bones, clavicle, &c. 



