328 



HUMAN ANATOMY. 



Fig 



Glenoid cartilage 



Head of 

 metacarpal 

 bone 



Insertion of 

 ext. commun. 

 digitorum 



Outer side of right forefinger 



phalangeal joint is opened. 



The metacarpo- 



springs from little hollows on the sides of the heads of the metacarpals. Longi- 

 tudinal fibres are distinct at the sides, if sought for from within the joint. The cap- 

 sule is strengthened on the palmar surface by fibrous or fibro-cartilaginous plates, — 

 \hQ glenoid carti/ages, — which form the beginnings of the floor of the canals for the 



flexor tendons (Fig. 350). These plates are 

 firmly fastened to the bases of the phalanges, 

 whose motions they follow, and loosely to the 

 metacarpals. In the thumb the glenoid plat€ 

 amounts to little or nothing, as the palmar 

 aspect of the joint is chiefly covered by the two 

 sesamoid bones, which are firmly held near 

 together by transverse fibres. When sesamoids 

 are present in the other joints, they are lost in ' 

 the fibrous tissue at the sides of these plates. 

 The glenoid cartilages of the four inner fingers 

 are attached to one another by a series of bands 

 of little strength, — the transverse metacarpal 

 ligament (Fig. 351). 



The articular surface of the metacarpal is 

 in the main convex and that of the phalanx 

 concave. They do not make a true ball-and- 

 socket joint, for the long axis of the latter is 

 transverse and at right angles to that of the 

 former, which, moreover, is much broader at 

 its palmar than at its dorsal end. As the 

 glenoid disks are parts of the floors of the 

 canals for the tendons diverging from the mid- 

 dle of the wrist, those of the second and fifth fingers are not squarely placed, but 

 incline to the middle of the hand. 



Movements. — When the finger is straight, it can be moved laterally, a little 

 backward, and flexed, as well as circumducted. It can, on the dead hand, be 

 slightly rotated ; but this motion does not occur m life. When it is fully flexed, 

 lateral motion is impossible owing to the tenseness of the capsule, which has occurred 

 in two ways, — partly from the fact that in flexion the phalanx rests on the broadest, 

 instead of the narrowest, part of the head, and because, the depressions for the 

 origins of the strongest lateral 



parts being near the dorsum, Y\g. 350. 



these are stretched when the 

 phalanx has travelled round the 

 palmar prominence of the head. 



The interphalangeal ar- 

 ticulations differ from the pre- 

 ceding by the peculiarities of the 

 articular ends and the greater 

 relative strength of the lateral 

 parts of the capsules. The gle- 

 noid cartilages are small. There 

 is no lateral motion. They are 

 the purest hinge-joints in the 

 body. 



The Surface Anatomy 

 of the Wrist and Hand. — 

 The joint between the forearm 

 and the carpus can be approxi- 

 mately indicated by a line either 

 on the back or the front, but more accurately on the former, starting from the *■ 

 head of the ulna, running nearly transversely, but with a slight upward bend, 

 to near the radial styloid, and then sweeping downward to its tip. The first row of 

 carpal bones can be made prominent on the back by flexing the wrist. The. hollow 



Transverse metacarpal ligament 



Metacarpals 



Head of 

 metacarpal 

 bone 



Phalanges 



Palmar aspect of right metacarpo-phalangeal joints, 

 flexor tendons opened. 



Glenoid cartilages 



Sheaths for 



