TO NORMAL HISTOLOGY. 



are the cartilage cells, each inclosed in a thick capsule. Make drawings 

 of all cartilage structures. 



IX. BONE. 



Bone is a compact, hard form of connective tissue. It comprises 

 two varieties spongy and compact. The spongy form occurs in the 

 v.'itebra* and the ends of the long bones. Compact bone is formed 

 from the spongy variety by the deposit of lamellae in the intrat rabec- 

 ular spaces. It is found chiefly in long bones between the articular 

 ends. A bone comprises three characteristic structures viz., the 

 periosteum, the lone-proper, and the marrow. 



The periosteum consists of two layers, the fibrous layer of dense 

 fibrous connective tissue which, as a protecting sheath, covers the 

 outer surface, and the osteogenetic layer, a somewhat loose struc- 

 ture, rich in cells and blood-vessels. This layer is so called because 

 it assists in forming bone. Its cells eventually become the osteo- 

 blasts, which are the bone builders. There are slender portions of 

 the periosteum which project into the bone proper. They are called 

 the perforating fibers of Sharpey. They are fibers of the periosteum 

 which have failed to ossify. 



The bone-proper is composed of cartilage and the carbonate and 

 phosphate of lime. Structurally considered, it comprises the Haver- 

 sian systems, the inter-Haversian systems, and the fundamental 

 lamellce. A Haversian system comprises the Haversian canal, the 

 lamellw, lacunae, canaliculi, and the bone cells. The Haversian 

 canal is a minute channel, from 20 // to 100 >j. in diameter, extend- 

 ing longitudinally and opening upon both the inner and outer sur- 

 face of the bone-proper. It contains an extension of the marrow, 

 and is rich in blood-vessels, cells, and lymphatics. 



The lamellae are plates of bone substance formed in the spaces 

 between the lacuna? and arranged concentrically around the canals. 

 The lacunae are the cavities which contain the bone cells. The cavi- 

 ties which are excavated by and contain the osteoclasts are called 

 How ship' s lacunw. The canaliculi are the slender tubes which ra- 

 diate from the lacuna? and serve as lymph channels, distributing nu- 

 trient fluids throughout the Haversian system. They anastomose 

 with each other and are connected with the canals. The bone cells 

 are the corpuscles within the lacunae. They send out processes into 



