334 THE ABTICULATIONS OK JOINTS. 



ARTICULATIONES DIGITORUM MANUS. 



Interphalangeal Joints. Of these joints there are two for each finger and 

 one for the thumb. They all correspond, in being ginglymus diarthroses in which 

 the trochlear character of their articular surfaces is associated with one axis of 

 movement directed transversely. 



In their general arrangement they correspond with each other, and to a large 

 extent with the metacarpo-phalangeal series already described. Each is provided 

 with a definite articular capsule (Fig. 312), of which the volar and cord-like lateral 

 portions are well marked, while on the dorsal aspect the extensor tendons act as the 

 chief support. The volar portions contain fibrous plates of considerable thickness, 

 and are attached to the two collateral ligaments and to the intervening rough 

 surface on the distal phalanges, while their proximal margins are not attached to 

 bone. Each ligament has its lateral margins prolonged proxirnally to the adjacent 

 sharply defined lateral ridges on the phalangeal shafts. 



The collateral ligaments (Fig. 312) are strong, rounded, short bands, continuous 

 with the preceding, and attached to the non-articular sides of adjacent heads and 

 bases of the phalanges. 



Each joint possesses a synovial stratum which lines its fibrous stratum, but its 

 arrangement presents no special peculiarity. The epiphyseal lines of the bases of 

 the phalanges are extra-capsular. 



MOVEMENTS OF THE CARPAL, INTERMETACARPAL, METACARPO-PHALANGEAL 

 AND INTERPHALANGEAL JOINTS. 



The amount of movement which is possible at individual joints of the intercarpal, inter- 

 metacarpal, and carpo-metacarpal series is extremely limited, both on account of the interlocking 

 nature of the articular surfaces and the restraining character of the ligamentous bands. Taken 

 as a whole, however, the movements of the carpus and metacarpus enable the hand to perform 

 many varied and important functions. This is largely due to the greater mobility of those joints 

 on the radial and ulnar borders of the hand, as well as to the general elasticity of the arches 

 formed by the carpus and metacarpus. These conditions particularly favour the movements of 

 opposition and prehension. In the opposite direction, i.e. when pressure is applied from the 

 volar aspect, the metacarpal and carpal arches tend to become flattened, but great elasticity is 

 ^mparted by the tension of the various ligaments. 



The four medial metacarpo-phalangeal joints are ball-and-socket joints, and movements of 

 velar-flexion and extension are freely performed about a transverse axis. In exceptional cases 

 a certain amount of dorsi-flexion is possible. About an antero -posterior axis movements occur 

 which are usually referred to the middle line of the hand, and hence called abduction and 

 adduction, but in consequence of the difference in the width of the articular surface on the dorsal 

 and volar aspects of the heads of the four medial metacarpal bone's it is only possible to .obtain 

 abduction when the joints are extended, while in the flexed position the joints become locked and 

 abduction is impossible. 



The movements of the index finger are less hampered than in the case of the others, but 

 each of them can perform a modified kind of circumduction. 



The metacarpo-phalangeal joint of the thumb and all the interphalangeal joints are uniaxial 

 or hinge-joints acting about a transverse axis, which permits of volar-flexion and extension 

 being freely performed, but dorsi-flexion is, as a rule, entirely prevented by the volar and lateral 

 ligaments. 



AKTICULATIONES ET LIGAMENTA CINGULI 

 EXTREMITATIS INFERIORIS. 



Articulations and Ligaments of the Pelvis. Although we may consider the 

 pelvis as a separate part of the skeleton, yet it is essential to remember that the 

 bones which enter into its composition belong to the vertebral column (sacrum, 

 coccyx) and the lower limb (hip bone). Accordingly, the articulations, with their 

 corresponding ligaments, may be arranged as follows : 



(a) Those by which the segments of the coccyx are joined together (already 



described, v. p. 310) ; 



(6) That by which the sacrum articulates with the coccyx (already de- 

 scribed, v. p. 309) ; 



