10 PRACTICAL ANATOMY. 



bones, are of different degrees of density ; the outer table, 

 less dense, is tough and elastic ; the inner is denser and 

 harder, and consequently brittle. The flat bones are 

 used mainly for protection, and also afford broad surfaces 

 for muscular attachment. 



Irregular bones are extremely irregular in outline, 

 and commonly consist of a shell of dense bone inclosing 

 spongy tissue, the interstices of which are filled with red 

 marrow. 



Bones present certain points for examination, ele- 

 vations and depressions, ridges and grooves, surfaces, lines, 

 foramina. A blunt elevation is called a tubercle or 

 tuberosity ; a depression may be slight or pit-like or deep, 

 or shallow and extensive, when it is designated a fossa. 

 Ridges may be rounded or sharp ; in the latter case they 

 are called crests. Grooves may be shallow, as the mus- 

 culo-spiral groove on the humerus, or deep. Surfaces 

 may be rough or smooth. Lines may be rough, sharp, 

 spiral, or broad. Besides these, a number of other terms 

 are employed: thus, the spine is a sharp, thorn-like 

 process ; a trochanter, a huge blunt elevation for the 

 attachment of muscles ; condyles are oblong elevations 

 of bone covered with cartilage, arranged in pairs ; an 

 articular surface is a plane, of more or less extent, cov- 

 ered with cartilage. In the growing skeleton the shafts 

 of many bones are separated from their extremities by 

 layers of cartilage ; such an extremity constitutes an 

 epiphysis, which remains separated from the shaft until 

 both have attained their full development, when the layer 

 of cartilage ossifies. Where a blunt process of bone grows 

 out from the shaft it is called an apophysis. If the ex- 

 tremity of a bone forms a single rounded prominence, 

 covered with cartilage, it is called a head ; a constriction 

 just below the head of a bone is known as the neck. 



