36 HUMAN PHYSIOLOGY. 



connective tissue surrounding the cartilage. By means of these channels, 

 nutritive fluid can permeate the entire structure. Hyaline cartilage is 

 found on the ends of the long bones, where it enters into the formation 

 of the joints; between the ribs and sternum, forming the costal cartilage, 

 as well as in the nose and larynx. 



2. White fibro-cartilage, the ground substance of which is pervaded by 

 white fibers, arranged in bundles or layers, between which are scattered 

 the usual encapsulated cells. White fibro-cartilage is tough, resistant, 

 but flexible, and is found in joints where strength and fixedness are re- 

 quired. Hence it is present between the vertebrae, forming the inter- 

 vertebral discs, between the condyle of the lower jaw and the glenoid 

 fossa, in the knee-joint, around the margin of the joint cavities, etc. In 

 these situations it assists in maintaining the apposition of the bones, 

 in giving a certain degree of mobility to the joints, and in diminishing the 

 effects of shock and pressure imparted to the bones. 



3. Yellow fibro-cartilage, the ground substance of which is pervaded by 

 opaque, yellow elastic fibers, which form, by the interlacing of their 

 branches, a complicated network, in the meshes of which are to be found 

 the usual corpuscles. As these fibers are elastic, they impart to the 

 cartilage a very considerable degree of elasticity. Yellow fibro-cartilage 

 is well adapted, therefore, for entering into the formation of the external 

 ear, epiglottis, Eustachian tube, etc. structures which require for their 

 functional activity a certain degree of flexibility and elasticity. 



Osseous Tissue. Osseous tissue, as distinguished from bone, is a member 

 of the connective-tissue group, the ground substance of which is permeated 

 with insoluble lime salts, of which the phosphate and carbonate are the 

 most abundant. Immersed in dilute solutions of hydrochloric acid, they can 

 be converted into soluble salts and dissolved out. The osseous matrix left 

 behind is soft and pliable. When boiled, it yields gelatin. 



A thin, transverse section of a decalcified bone, when examined micro- 

 scopically, reveals a number of small, round or oval openings, which repre- 

 sent transverse sections of canals which run though 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. 



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 com- 

 municate freely with one another. The Haversian canals, with their asso- 

 ciated lacunas and canaliculi, form a system of intercommunicating passage, 



