ANATOMY 



OF THE 



. DOMESTIC FOWL 



OSTEOLOGY 



Osseous Structure. — ^Bone is structurally modified connective 

 tissue which has become hard by being impregnated with calcium 

 salts. 



Kinds of Bone Tissue. — There are two kinds of bone tissue: 

 substantia compacta, or compact bone tissue; and substantia spon- 

 giosa, or spongy, cancellous bone tissue. 



Compact Bone Tissue. — The compact bone tissue forms the hard 

 outer layer of all bones. It is thickest in the shaft and becomes thin 

 toward the extremities. Through the compact bone tissue approxi- 

 mately parallel with the longitudinal axis of the bone, run canals 

 called Haversian canals, through which pass blood and lymph ves- 

 sels for the nourishment of the bone and nerves. The Haversian 

 canals are surrounded by concentric lamella. The spaces between 

 the cylinders thus formed are filled with interstitial lamellae; and 

 both the exterior surface of the bone and the interior surface sur- 

 rounding the medullary canal, are built up of peripheral, or circum- 

 ferential lamellae. Between the lamellae, somewhat irregularly 

 placed, are minute reservoirs, called lacuna, which contain bone 

 corpuscles. From the lacunae radiate minute canals, or canali- 

 culi, which maintain circulation through the bone substance, and 

 which communicate with the Haversian canals. Complex anasto- 

 moses exist among the canaUculi. Still other channels for the pas- 

 sage of blood-vessels are Volkmann's canals which pierce the periph- 

 eral lamellae, thus allowing vessels to pass from the periosteum to 

 the Haversian canals. Similar channels afford communication 

 between the inner Haversian canals and the medullary cavity. 



The entire structure composed of an Haversian canal, its sur- 

 2 17 



