io6 HUMAN ANATOMY. 



Parts of Bones. — The following are some of the names applied to features 

 of bone : 



A process is a general term for a projection. 



A spine or spinous process is a sharp projection. 



A tuberosity is a large rounded one, a tubercle is a small one, either rounded or 

 pointed. 



A crest is a prominent ridge. 



A head is an enlargement at the end of a bone, in part articular. 



A neck is a constriction below a head. 



A condyle is a rounded articular eminence, generally a modification of a cylinder. 



A. fossa is a pit. 



A glenoid cavity is a shallow articular depression. 



A cotyloid cavity is a deep one. 



A sulcus is a furrow. 



A foramen is a hole, in the sense of a perforation. 



A sinus is the cavity of a hollow bone, equivalent to antrum. It is used also 

 to designate certain grooves for veins in the cavity of the cranium. 



In addition to the cartilage-covered articular surfaces proper, the fresh bones 

 show in some places a plate of cartilage quite like one for a joint; such plates serve to 

 lessen the friction of a tendon playing over the bone. In other places a look of pecul- 

 iar smoothness is conferred by the presence of a bursa, although cartilage is wanting. 



Sex of Bones. — Female bones are characterized in general by: (a) a greater 

 slenderness; C<^) a smaller development of processes and ridges for muscular attach- 

 ment'; (<:) and, most important of all, the small size of the articular surfaces. These 

 guides usually suffice to determine the sex of the chief bones; some, especially those 

 of the pelvis, possess characteristic sexual differences of form. 



Age of Bones. — At birth the long bones have cartilaginous ends in which, 

 with one or two exceptions, the centres of ossification have not yet appeared. Many 

 bones at this period still consist of several pieces which ultimately fuse. The shape 

 and proportions are in some cases different from those of the adult. Sexual differ- 

 ences cannot in most cases be determined. During the first years new centres of 

 ossification appear, distinct pieces unite, and the proportions change from the type 

 of the infant to that of the child. Towards puberty important further changes in 

 proportion occur, and sexual differences develop. 



After puberty the bones present three stages, — adolescence, maturity, and senility. 

 In the first the union of the epiphyses is going on ; after this has taken place the 

 line of separation is visible for a time, but gradually disappears. Our knowledge of 

 the time at which these changes occur enables us to determine the age of the skel- 

 eton. The long period of maturity presents little that allows of a precise estimate 

 of age. The separate bones of the vault of the cranium gradually fuse into one. 

 The senile skeleton in its extreme stage is very striking. There is a general atrophy 

 of the bones both within and without, those of the face becoming in parts of papery 

 thinness ; not only the cavities within the cranial bones become larger, but also the 

 spaces within the cancellous tissue inside the bones, due to the partial absorption of 

 the spongy substance. The only bones, however, which show a distinct change of 

 form are the jaws, and this is a secondary result of the loss of the teeth. In many 

 cases, however, senile absorption and atrophy do not occur, except, perhaps, in the 

 head ; it may be, therefore, absolutely impossible to distinguish a long bone of an 

 old subject from one of an individual in early maturity. The periods at which the 

 age of bones is most often a matter of medico-legal inquiry are at the time of birth 

 and in childhood and youth. The dates of the first appearance of ossification in 

 the various bones are the criteria for the .first. These are to be used, however, with 

 great caution, since variation is considerable. The information to be derived from 

 consideration of the general development of the body is perhaps of equal value. 

 The same holds good for childhood and adolescence. The particular point on which 

 the writer holds strong views, based on his own observations, differing from those 

 generally accepted, is as to the time of union of the epiphyses at the end of ado- 



' Dwight • American Journal of Anatomy, Vol. iv., 1904. 



