THE CONNECTIVE TISSUES. 



55 



which represent transverse sections of canals which run through the 

 bone, for the most part in a longitudinal direction, though frequently 

 anastomosing with one another. These so-called Haversian canals 

 in the living state contain blood-vessels and lymphatics. (See 

 Fig. 14.) 



Around each Haversian canal is a series of concentric laminae, 

 composed of white fibers. Between every two laminae are found small 

 cavities (lacunae), from which radiate in all directions small canals 

 (canaliculi), which communicate freely with one another. The 

 Haversian canals, with their associated lacunae and canaliculi, 

 form a system of intercommunicating passages, which circulate 

 lymph destined for the nourishment of bone. Each lacuna 

 contains the bone corpuscle, which bears a close resemblance to the 



Periosteum. 



Outer ground lamellae. 



Haversian canals. 



Haversian lamellae. 



Interstitial lamellae. 

 Inner ground lamellae. 



Marrow. 



FIG. 14. FROM A CROSS-SECTION or A METACARP OF MAN. X 50. The Haversian 

 canals contain a little marrow (fat-cells). Resorption line at h. 



usual branched connective-tissue corpuscle, and whose function 

 appears to be the maintenance of the nutrition of the bone. 



The surface of every bone in the living state is invested with a 

 fibrous membrane, the periosteum, except where it is covered with 

 cartilage. The inner surface of this membrane is loose in texture, 

 and supports a fine plexus of capillary blood-vessels and numerous 

 protoplasmic cells the osteoblasts. As this layer is directly con- 

 cerned in the formation of bone, it is spoken of as the osteogenetic 

 layer. 



A section of a bone shows that it is composed of two kinds of 

 tissue compact and cancellated. The compact is dense, resembling 

 ivory, and is found on the outer portion of the bone; the cancellated 

 is spongy, and appears to be made up of thin, bony plates, which 

 intersect one another in all directions, and is found in greatest abun- 



