BONE. 41 



the articular cartilages of some joints, as the knee and the wrist ; 

 connecting , as between the bodies of the vertebrae ; circumferential, 

 as in the cotyloid cavity of the hip-joint, which it makes deeper ; 

 and stratiform, where it lines grooves in bone through which 

 tendons pass. It also occurs in some tendons, as in that of the 

 peroneus longus. 



Yellow Elastic Cartilage (Fig. 32). The presence of elastic 

 fibers in the matrix is the distinguishing feature of this variety of 

 cartilage, which is found in the pinna of the ear, the Eustachian 

 tube, the epiglottis, and the cornicula laryngis. 



Cellular Cartilage. This kind is made up almost wholly of cells ; 

 sometimes fine fibers are present. The only structure in which it 

 is found in the human body is the chorda dorsalis or notochord of 

 the embryo. 



Chemical Composition of Cartilage. The following analyses 

 were made by Hoppe-Seyler, and represent parts per 1000 : 



Costal Cartilage. Articular Cartilage. 



Water ; . 676.6 735.9 



Solids, organic 301.3 248.7 



Solids, inorganic . . . 22.0 15.4 



999.9 1000.0 



Organic Solids of Cartilage. The cells contain, besides the 

 proteid contents of cells generally, fat and glycogen. The matrix 

 contains chondrigen, which on boiling yields chondrin. This is 

 the generally accepted theory as to cartilage, but the most recent 

 analyses seem to show that chondrin is not a simple substance, but 

 a mixture, and that in the matrix are four substances : 1. Col- 

 lagen ; 2. An albuminoid, which exists only in later adult life, and 

 is like elastin, but contains more sulphur ; 3. Chondromucoid ; and 

 4. Chondroitin-sulphuric acid. 



Inorganic Solids of Cartilage. Potassium and sodium sul- 

 phates, sodium chlorid, and sodium, calcium, and magnesium 

 phosphates represent the inorganic class of physiologic ingredients 

 of cartilage. 



Perichondrium. This is a fibrous membrane which envelops 

 cartilage except at the articular ends of bones : it contains blood- 

 vessels, which assist in nourishing the cartilage. 



Bone. There are two varieties of bone : compact and can- 

 cellous or cancellated. The former is firm and dense, and occurs 

 on the exterior of bones ; the latter is spongy and more open in 

 structure, and occupies the interior. The differences between the 

 two are not such as to justify their being regarded as two distinct 

 varieties, for in all essential points they are identical. Practically, 

 however, it seems wise to describe them separately. When a 

 cross-section of a bone is examined under the microscope (Fig. 33) 

 Haversian canals are seen, averaging 0.05 mm. in diameter : 



