ii6 Anatomy of Skeleton 



The last phalanges have a distal expansion that lies under the nail, but its greater 

 thickness is on the palmar surface, where it is roughened by the attachment of the 

 fibre-fatty pad that makes the palmar finger-tip. 



The strong phalanges of the thumb are in general similar to the first and last 

 phalanges of the other fingers, but it should be noticed that the base of the first phalanx 

 exhibits a slight central prominence in front which resembles the inter-condylar point 

 on the bases of the second phalanges of the other fingers. This is probably associated 

 with the large size of the sesamoids in the joint and the fact that the intercornual 

 notch in the first metacarpal is more horizontally placed than in the other bones, so 

 that the phalanx fits, in its front part, for practical purposes on two badly-formed 

 condyles. 



The phalanges of the hand are much stronger than those of the foot, for they are 

 used as opponents in grasping, whereas little weight is thrown on the foot bones, 

 except in the case of the big toe. So the appearance of the two classes of bones, con- 

 forming with this, is enough (Fig. 85) to enable one to distinguish between them at 

 a glance. 



Development of Bones of Hand. 



All the bony elements of the hand are preformed in cartilage, and in the case 

 of the carpus the cartilaginous units are usually greater in number than the bony. 

 Possibly this may have an atavistic significance : in lower vertebrate forms the typical 

 carpus consists of two rows, a proximal containing three elements, radial, ulnar, and 

 intermediate, and a distal with five " carpalia," each one supporting a metacarpal and 

 numbered from without inwards : between the two rows is placed an " os centrale," 

 round which the others might be said to be grouped (see Fig. 157). 



In the human cartilaginous carpus the os radiale is represented by the 

 scaphoid, the intermedium by the semilunar, and ulnare by cuneiform : the pisi- 

 form is usually regarded as of the nature of a sesamoid, although this view is not 

 incontestable. 



The five carpalia are represented by (i) Trapezium, (2) Trapezoid, (3) Os Magnum, 

 (4) and (5) Unciform : the double nature of the unciform is indicated by the facts 

 that it supports two metacarpals, is chondrified from two cartilaginous centres, 

 and is said to be ossified also from two centres. The os centrale is represented by 

 a small cartilaginous nodule usually present in the embryo, which either becomes 

 divided and disappears later or joins with one of the other elements, usually the 

 scaphoid. 



Many irregular and differing " elements " have been described from time to time 

 in association with the carpus : of these the most constantly found are the separated 

 styloid process of the 3rd metacarpal and (rarely) a small ossicle on the outer side of the 

 scaphoid, the radiale externum. In many cases the additional so-called " elements " 

 are ununited results of old fractures of the carpus. 



The trapezium is at first smaller than the trapezoid, and the hook of the unciform 

 is developed in cartilage after the body. 



The carpus is cartilaginous at birth, but there is occasionally a centre in the os 

 magnum. This centre appears as a rule a few months after birth, and the whole 

 carpus, with the exception of the pisiform, is ossified by the sixth or seventh year : the 

 pisiform centre does not appear until about ten to twelve years. The centres appear 

 in a more or less definite order, and for practical purposes the times shown in the table 

 below may be taken as approximately correct. It is to be noted that the centres 

 appear from a few months to a year earlier in the female hand : 



