BONE 93 



of the roof of the skull they form an interlacing network (Schulz). Perfo- 

 rating fibers, such as were described in the preceding paragraph, may 

 arise from this layer; and others, both white and elastic, derived from ten- 

 dons, may pass through it into the bone. In this way the tendons acquire 

 a very firm insertion. The cells of the inner layer of the periosteum are 

 spindle-shaped or flattened connective tissue cells, together with the more 

 cuboidal osteoblasts which rest against the bone. In young bones these 

 are so numerous as to form a third layer of the periosteum. In the 

 adult they are few in number, but are capable of proliferation, and to- 

 gether with those in the endosteum. they are the source of new bone after 

 injury. The periosteum, in bodies which have been kept a week at 15 

 C., is said to be capable of producing bone when transplanted to another 

 body; and after operations in which a shaft of bone has been shelled 

 out from its periosteum, a new shaft may be formed. 



Beneath the periosteum, as seen in the cross section of the shaft of a 

 long bone (Fig. 80) , there are layers or lamellae of bone which are parallel 



Suture. Perforating fibers. Periosteal lamellae. 



/ I 



Blood vessel. Volkraann's canal. Haversian canal. 



FIG. 79. SECTION ACROSS A SUTURE IN THE SKULL OF AN ADULT. 

 Prepared by Bielschowsky's method. X 80. 



with the surface. These are the "outer ground lamellae" or periosteal 

 lamella. They are traversed by Sharpey's perforating fibers and by small 

 blood vessels lodged in the so-called Volkmann's canals. The bone 

 cells occupy lacunae, situated between the lamellae, and in Fig. 80 they 

 are seen as small spots. In the lowest part of the figure, a portion of 

 the marrow has been included. The marrow is surrounded by the 

 endosteum, external to which are the "inner ground lamellae" or endosteal 

 lamella. These are parallel with the inner surface of the bone. 



Between the periosteal and the endosteal lamellae there is a dense 

 mass of matrix unlike anything found in embryonic bone. Scattered 

 through it, numerous blood vessels are seen in cross section. Each 

 vessel is surrounded by concentric lamella which present a very charac- 



