42 



GENERAL ANATOMY OF THE SKELETON 



lamellae, lacuna 3 , and canaliculi is seen, though not so plainly as in the ordinary section. The 

 animal basis is largely composed of ossein, or fat collagen. When boiled with water, especially 

 under pressure, fat collagen is almost entirely resolved into gelatin. 



The earthy part may be obtained by calcination, in which process the animal matter is com- 

 pletely burned out. The bone will still retain its original form, but it will be white and brittle, 

 will have lost about one-third of its original weight, and will crumble upon the slightest pressure. 

 The earthy matter confers on bone its hardness and rigidity, and the animal matter its tenacity. 

 The mineral matter consists chiefly of calcium phosphate, forming about two-thirds of the 

 weight of bone. 



Ossification and Growth of Bone. For the early development of the skeleton the 

 reader is referred to text-books on embryology. Embryonic connective-tissue cells of the meso- 



blast develop membrane. Membrane may become 

 bone directly or cartilage may be deposited, which 

 cartilage by the process of ossification is changed into 

 bone. The tissue which is eventually to become bone 

 contains cellular elements which evolve into osteo- 

 blasts, or bone-forming cells. Osteoblasts exist in the 

 connective tissues which become bone by intramem- 

 branous ossification, and in the deeper layers of the 

 tissue called perichondrium which invests cartilage 

 and which becomes the osteogenetic layer of the peri- 

 osteum. In view of the fact that in the fetal skeleton 

 some bones are preceded by membrane (parietal bones, 

 frontal bone, upper part of tabular portion of occipital 

 bone, most of the bones of the face), and others are pre- 

 ceded by rods of cartilage (the long bones), two kinds 

 of ossification are described viz., the intramembra- 

 nous and the intracartilaginous. 



Intramembranous Ossification. In the case of 

 bones which are developed in membrane no cartilagi- 

 nous mould precedes the appearance of the bone tissue. 

 The membrane, which occupies the place of the future 

 bone, consists of white, fibrous connective tissue, and 

 ultimately forms the periosteum. At this stage it is seen 

 to be composed of fibres and granular cells in a matrix. 



The outer portion is more fibrous, while internally the cells or osteoblasts predominate; the whole 

 tissue is quite vascular. At the outset of the process of bone formation a little network of bony 

 spicules is first noticed radiating from the point or centre of ossification. When these rays of 



zpt 



FIG. 9. Schematic diagram, showing epi- 

 physis and diaphysis and line of ossification. 

 Ep. Epiphysis of endochondral bone. _ zpt. 

 Zone of proliferation, zc. Zone of calcifica- 

 tion, ca. Cartilage. (Poirier and Charpy.) 



Union a - 

 adjaceii 

 spiculex 



Otteoblasls .<' 



Osteogenetic 

 fibres. 



deposit 

 between the 

 fibres. 



Bony 



spicules. 



FIG. 10. Part of the growing edge of the developing parietal bone of a fetal oat. (After .T. Lawrence.) 



growing bone are examined with a microscope they are found to consist at their growing point 

 of a network of fine, clear fibres and granular corpuscles, with an intervening ground substance 

 (Fig. 10). The fibres are termed osteogenetic fibres, and are made up of fine fibrils differing 



