1 8 ANATOMY OF THE DOMESTIC FOWL 



rounding lamellae, lacunae, and canaliculi, with their contained 

 vessels, is called an Haversian system. 



Cancellous Bone Tissue. The cancellous bone tissue forms the 

 bulk of the short, flat, and irregular bones and of the extremities 

 of the long bones. It consists of delicate bony plates and spicules, 

 which intercross in various directions. The spaces between', these 

 plates and spicules, called cancelli, are occupied by marrow except in 

 the bones that are pneumatic. The blood-vessels, lymphatics, and 

 nerves course through this marrow but are not arranged in an Ha- 

 versian system. 



PIG. i. Longitudinal section of compact bone of the femur of the hen. I, 

 Haversian canals. 2, Lacunae with their canaliculi. 



The Periosteum. Covering the surface of bone, except at the 

 articular surface where it is covered with cartilage, is a membrane, 

 the periosteum, which consists of two layers: an outer, fibrous, 

 protective layer, and an inner, cellular, osteogenic layer. The outer 

 layer consists principally of white fibrous tissue. The inner layer 

 contains many more connective-tissue cells, which gradually be- 

 come more closely aggregated as we proceed toward the osseous 

 surface; but there is no sharply defined line of demarcation between 

 the two periosteal layers. 



