PLATE Till— Continued. 



hence the dark appearance of the cartilage, especially near the 

 advancing ossification. The secondary osseous deposit near the 

 centre of the bone has not been represented of sufiBcient relative 

 thickness. Drawn under a magnifying power of about 

 80 diameters. 



Fig. 3. — Longitudinal section through the subperiosteal thickening (encoche 

 d'ossification). Drawn under a power of about 200 diameters. 

 The preparation was stained with logwood and eosin. The osteo- 

 blastic tissue and the osteogenic fibres are shown. One or two 

 blood-vessels are seen cut across. On the left is the cartilage, 

 which is quite sharply marked off from the tissue of the encoche. 

 Only the more superficial fibres are traceable into the superficial 

 part of the cartilaginous head ; the rest terminate for the most 

 part before reaching the cartilage. 



Fig. 4. — Represents a very small piece of the foregoing preparation under 

 a higher magnifying power (400 diameters). The mode in which 

 the angular osteoblasts fit in between and are applied to the 

 osteogenic fibres is shown. The adjacent cartilage is on the left 

 hand of the figure, b, bone ; c, cartilage ; o,f, osteogenic fibres. 



Fig. 5. — Transverse section of a bone similar to Fig. 2, and drawn to the 

 same scale; (ic), part ossified in cartilage; {im), part ossified in 

 membrane; {p), sub-periosteal layer; (o), osteogenetic fibres. 



PLATE VIIL 



Fig. 1. — A piece of the growing parietal of a foetal cat, 1^ inch long. 

 The blood-vessels and investing membranes were removed, but 

 the osteogenic fibres and osteoblasts were left. The osteoblasts 

 were not apparent, on account of the lowness of the magnifying 

 power employed. The growing edge is seen to be fringed with 

 osteogenic fibres ; the intercrossing of these can be seen. One 

 or two islands of ossified tissue are seen united to the main bony 

 mass by bridges of osteogenic fibres. Slightly magnified. 



Fig. 2. — The extremities of two osseous spicules, terminating in bunches 

 of nearly straight, stiff-looking, osteogenic fibres. Some of the 

 fibres of the two spicules are continuous into one another ; 

 others take directions oblique to one another, and tending in the 

 progress of growth to intercross. The osteoblasts appear as if 

 entangled amongst the fibres ; many of theni are seen to be 

 applied to the fibres along a part of their course. The newly- 

 deposited earthy matter is in the form of minute globules, giving 

 a granular appearance to the new bone ; as the intermediate 

 substance between the globules becomes filled up by calcific 

 deposit, the bone acquires a clearer aspect (as in the lower part 

 of the figure. From a part of the growing margin of the bone 

 represented in Fig. 1. Drawn under a magnifying power of 

 400 diameters. 



