TISSUES OF THE BODY. 



251 



outline of the view which formerly obtained in regard to the supposed metamorphosis 

 of cartilage : During the process of ossification, bony earths are deposited in the car- 

 tilage ; the cells of the latter change, according to the third theory mentioned above, 

 into bone corpuscles ; while their secondary envelopes fuse into the intercellular sub- 

 stance, forming thus the ground-mass of the bone. The origin of the medullary 

 cavities and canals was set down to a process of absorption and resolution in the 

 tissue undergoing this change. The formation of the lamellae remained more or less 

 unexplained, and that of the canaliculi was but unsatisfactorily touched on. We owe 

 much to Bruch, Baur, and more than all, to H. Mullcr (Zeitschrift fur wissensch. 

 Zoologie, Vol. 9, p. 147), for having shown this view of the supposed transformation 

 of cartilage into bone to be erroneous, working on Sharpey's premises. 



146. 



Now, although from the foregoing section we must perceive that bone 

 is not formed by an immediate trans- 

 formation of cartilage, nevertheless, in 

 order to comprehend rightly the pro- 

 cess of ossification in portions of the 

 skeleton preformed in the latter, a 

 knowledge of the texture prevailing in 

 the same is indispensable. Eeference 

 has already been made ( 106 and 

 107) to the calcification and softening, 

 as well as to the arrangement and 

 nature of the cells of cartilage. The 

 various groupings of the latter are 

 represented in fig. 241, g, and 242 

 (above). 



Cartilage shows further, previous 

 to the commencement of ossification, 

 blood-vessels, which spring up at an 

 early period of foetal life, and are of 

 course of importance in the changes 

 about to take place. They grow from 

 the perichondrium in tufts into the 

 softening tissue. Around them a soft 

 immature connective- tissue is formed, 

 and thus canals are produced. This 

 is the so-called cartilage medulla, whose 

 cellular constituents were formerly 

 looked upon as descendants of the car- 

 tilage cells (although no one had ever 

 seen the transition). The boundary 

 of the medullary canals in the cartilage 

 is always sharply and suddenly defined 

 against the cells of the latter (fig. 241). 



Those broad irregular vessels just 

 mentioned require further examination, 

 both as regards their course and the 

 structure of their walls. 



In the condition just described, car- 

 tilage is prepared for calcification and 

 the formation of bone, closely follow- 

 ing on it. The latter commences, as 

 is well known, at certain definite spots, the points of ossification, or 



Fig. 241. Vertical section from the edge of 

 the ossifying portion of the diaphysis of a 

 metatarsus, from a f ostal calf 2' long ; after 

 Millier. a, ground-mass of the cartilage; 

 6, of the bone; c, newly-formed bone-cells 

 in profile, more or less imbedded in inter- 

 cellular substance; d, medullary canal in 

 process of formation with vessels and medul- 

 lary cells; e, /, bone-cells on their broad 

 HRpect; g, cartilage capsules arranged in 

 rows, and partly with shrunken cell-bodies. 



