THE UPPER LIMB 409 



The synovial membrane is peculiar to the joint. 



Arterial Supply. — The arteria princeps pollicis of the radial. 



Nerve-supply. — ^The median ner\^e. 



Movements. — The movements allowed are flexion, extension, abduction, 

 adduction, and circumduction. It is at this joint where the important move- 

 ment of opposition takes place, whereby the tip of the thumb can be opposed 

 in succession to the tip of each of the four inner fingers. 



Intermetacarpal Joints. — The basal intermetacarpal joints belong 

 to the class diarthrosis, and to the subdivision arthrodia. The 

 bones concerned are the inner four metacarpals, the first metacarpal 

 bone standing off from the second, with which it has no articula- 

 tion. The ligaments are dorsal, palmar, and interosseous. The 

 dorsal ligaments are composed of stout fibres, which pass trans- 

 versely between the contiguous aspects of the bases. The palmar 

 ligaments are similarly disposed in front. The interosseous liga- 

 ments are strong bundles which pass between the opposed surfaces 

 of the bases to which they are attached on the distal sides of the 

 articular facets. 



Nerve-supply. — ^The deep division of the ulnar nerve. 



Arterial Supply. — ^The palmar and dorsal interosseous arteries. 



The synovial membrane is a downward prolongation from that 

 of the carpus. 



The heads of the inner four metacarpal bones are connected by 

 the transverse metacarpal (deep transverse) ligament. It extends 

 transversely across the palmar aspects of the heads, and its fibres 

 are attached to the fibrous plates on the palmar surfaces of the 

 metacarpo-phalangeal joints. It receives the deep expansions of 

 the digital processes of the central division of the palmar fascia, 

 and the digital arteries and nerves pass in front of it, and the in- 

 terosseous muscles behind it. It is to be noted that the transverse 

 metacarpal ligament excludes the head of the first metacarpal bone, 

 whereas the corresponding ligament of the foot includes the head 

 of the first metatarsal. 



The synovial membranes from the inferior radio-ulnar joint down 

 to the intermetacarpal joints are five in number, as follows : 



1. Inferior radio-ulnar or membrana sacciformis. 



2. Radio-carpal. 



3. Pisiform. 



4. Carpal, composed of carpal proper, carpo-metacarpal, and 

 intermetacarpal portions, all continuous with one another. 



5. Carpo-metacarpal of the thumb. 



Metacarpo-phalangeal Joints. — These belong to the class diar- 

 throsis, and to the subdivision condylarthrosis, which is a modifi- 

 cation of enarthrosis or ball-and-socket joint. In each joint the 

 round head of a metacarpal bone articulates with the cup- shaped 

 depression on the proximal end of a first phalanx. 



Inner Four Metacarpo-phalangeal Joints. — Each of these joints 

 has three hgaments — two .lateral, and a palmar. The lateral 



