XIV." 



BONE AND ITS DEVELOPMENT. 



they also line, so that every spicule or surface of young bone is 

 covered by them. From them the bone-corpuscles are formed. 



(b.) The osseous tissue is stained red, and forms an anastomosing 

 series of trabeculae bounding large spaces Haversian spaces- 

 containing blood-vessels and marrow, and lined by osteoblasts. 

 Processes from the trabeculse project into the deeper layer of the 

 periosteum. At this stage a concentric arrangement of the lamellae 

 leading to the formation of Haversian systems has not yet taken 

 place. In the bone matrix, the bone-corpuscles (/), irregular, re- 

 fractive, nucleated cells, each lying in a lacuna. 



(c.) (H) Under the periosteum and in the spaces may be seen 

 larger multinucleated cells. 



Osteoclasts or Myeloplaxes (fig. 1 56, If). The cells are much 

 larger than the osteoblasts, con- 

 tain many nuclei, and lie in little 

 depressions of the bone eroded 

 by themselves. These depres- 

 sions are called Howship's 

 lacunas. These cells are con 

 cerned in the removal of bone. 



2. Intra-Cartilaginous For- 

 mation of Bone (L and H). 

 Decalcify in picric acid the pha- 

 langeal bones of a four-months 

 footus. Make longitudinal ver- 

 tical sections, stain in picro- 

 carmine, and mount in Farrant's 

 solution. 



(a.) (L) At the head of the 

 bone observe a mass of hyaline 

 cartilage (fig. 157), and lower 

 down bone, and where the two are continuous an irregular festooned 

 margin, the line of ossification. 



(b.) The cartilage at the upper part is hyaline, with the cells 

 small, and arranged singly or in groups, while deeper down the 

 cartilage-capsules are beginning to be arranged in rows, and below 

 this are larger cartilage-capsules with clearer contents, and a some- 

 what refractive matrix between them. 



(f.) Under this, the line of ossification, with its festooned 

 margin, are spicules of calcified cartilage passing downwards 

 towards the medullary cavity. In the bony part, the primary 

 medullary spaces, with their osteoblasts, blood-vessels, osteodasts, 

 and tho. newly-formed hone deposited on the calcified cartilage. 



(d.) Tho first none is formed under the, periosteum (fig. 157), by 

 means of the subperiosteal osteoblasts. As these osteoblasts 



FIG. 156. T.S. Fcctal Bone of Kitten, a, b. 

 Superficial and deep layers of perios- 

 teum; c. Layers of osteoblasts, with 

 Ic. Osteoclasts ; m. Matrix of bone ; I. 

 Lacunae, with bone-corpuscles. 



