CHEMICAL COMPOSITION OF BONE — DESCRIPTIVE TERMS 23 



ysis and the epiphysis. It is evident that so long as this cartilage persists and 

 grows, new bone may continue to be formed at its expense, and increase of length 

 is possible. When the epiphyseal cartilage ceases to grow, it undergoes ossifica- 

 tion, the bone is consolidated, and no further increase in length is possible. This 

 fusion takes place at fairly definite periods in the various bones, and it is of value 

 to know the usual times at which it occurs in the larger bones of the limbs at least. 



After the bones have reached their full size, the periosteum l^ecomes relatively reduced and 

 inactive so far as its osteogenic layer is concerned; the bone-forming function may be stimulated 

 by various causes, as is well seen in the healing of fractures and the occurrence of bony enlarge- 

 ments. 



CHEMICAL COMPOSITION OF BONE 



Dried bone consists of organic and inorganic matter in the ratio of 1 : 2 

 approximately. The animal matter gives toughness and elasticity, the mineral 

 matter hardness, to the bone tissue. Removal of the organic matter by heat does 

 not change the general form of a bone, but reduces the weight by about one-third, 

 and makes it very fragile. Conversely, decalcification, while not affecting the form 

 and size of the bone, renders it soft and pliable. The animal matter when boiled 

 yields gelatin. The following table represents the composition in 100 parts of ox 

 bone of average quality: 



Gelatin 33.30 



Phosphate of lime 57.35 



Carbonate of hme 3.85 



Phosphate of magnesia 2.05 



Carbonate and chlorid of sodium 3.45 



100.00 



PHYSICAL PROPERTIES OF BONE 



Fresh dead bone has a yellowish-white color; when macerated or boiled and 

 bleached, it is white. The specific gravity of fresh compact bone is a little over 

 1.93. It is very hard and resistant to pressure; a 5-millimeter cube of compact 

 bone of the ox will resist pressure up to 852 pounds, if the pressure be applied in 

 the line of the lamellae (Rauber). Its tensile strength is estimated to be nearly 

 twice that of oak. 



DESCRIPTIVE TERMS 



The surfaces of the bones present a great variety of eminences and depressions, 

 as well as perforations. The prominences and cavities may be articular, or non- 

 articular, furnishing attachment to muscles, tendons, ligaments or fascia. A 

 number of descriptive terms are used to designate these features, and the following 

 are some of those in general use: 



Process (Processus) is a general term for a prominence. 



A tuberosity (Tuber, Tuberositas) is a large, rounded projection; a tubercle 

 (Tuberculum) is a smaller one. 



The term trochanter is applied to a few prominences, e. g., the trochanters of 

 the femur. 



A spine (Spina) or spinous process (Processus spinosus) is a pointed projection. 



A crest (Crista) is a shar}) ritlge. 



A line (Linea) is a very small ridge. 



A head (Caput) is a rounded articular enlargement at the end of a bone; 

 it may be joined to the shaft by a constricted part, the neck (Collum). 



A condyle (Condylus) is an articular eminence which is somewhat cylindrical; 

 a non-articular projection in connection with a condyle may be termed an epi- 

 condyle. 



