CONNECTIVE TISSUE. 



239 



of a calcareous deposition. This occurs first in the middle of 

 the shaft, and gradually proceeds toward both extremities, vary- 

 ing considerably, both in time and extent, in different human 

 embryos and in different ani- 

 mal embryos. In specimens 

 decalcified by chromic acid, 

 the basis-substance, which 

 was the seat of a deposition 

 of lime-salts, readily takes 

 up the carmine stain. (See 

 Fig. 95.) 



The calcareous deposition 

 occurs only in the broad 

 masses of basis-substance be- 

 tween the territories, of the 

 cartilage corpuscles, in con- 

 sequence of which an elon- 

 gated reticular frame is visi- 

 ble, which at first surrounds 

 the territories of the cartilage 

 corpuscles, and deeper below, 

 in a nearly level line, it sur- 

 rounds the spaces filled with 

 medullary corpuscles. The 

 calcification is sharply de- 

 fined by pointed ends toward 

 the unchanged cartilaginous 

 portion. In the deeper por- 

 tions of the calcified frame 

 the first traces of newly 

 formed bone-tissue are no- 

 ticeable in the shape of 

 bright crescentic fields, at- 

 tached by their convex sur- 

 faces to the calcified frame. 

 This investment of bone soon 

 produces a continuous layer 

 around the frame at its bor- 

 ders toward the medullary 

 spaces. 



In the cartilaginous heads 

 of shaft-bones of human embryos, at a somewhat later period, a 



FIG. 95. HUMERUS OF A HUMAN EM- 

 BRYO, FIVE MONTHS OLD. SAGITTAL 

 SECTION. CHROMIC ACID SPECIMEN. 



C, rows of cartilage corpuscles in elongated 

 groups, due to their territories ; F, frame of calci- 

 ned basis-substance, around which, in the lower 

 portions, the first traces of bone-tissue are no- 

 ticeable ; M, medullary space, containing medul- 

 lary corpuscles. Magnified 300 diameters. 



