438 THE INFERIOR EXTREMITY 



or, in the cases of the metatarso-phalangeal joint of the great 

 toe, and occasionally of some of the other toes also, upon the 

 sesamoid bones developed in the plantar accessory ligament 

 (Fig. 197). When the joints are flexed the proximal end of 

 the distal bone moves to the plantar aspect of the distal end 

 of the proximal bone, and the extremities of the distal bones 

 are then covered only by the extensor tendons and the skin. 

 When the joints are flexed, therefore, they are easily opened 

 from the dorsal aspects by cutting transversely directly against 

 the heads of the proximal bones. The dissector should open 

 one or more joints in that manner. 



Each joint possesses the following ligaments : 



Capsula articularis, 

 Ligamenta collateralia, 

 Ligamentum accessorium plantare. 



Capsula Articularis. The fibrous stratum of the articular 

 capsule is deficient dorsally, and there the extensor tendons 

 lie in direct relation with the synovial stratum which lines the 

 interior of the fibrous stratum. At the sides the fibrous 

 stratum is blended with the collateral ligaments, and on the 

 plantar aspect with the plantar accessory ligament. 



Ligamenta Accessoria Plantaria. Each plantar accessory 

 ligament is a dense fibrous plate which is firmly attached to 

 the plantar aspect of the base of the distal bone of the joint, 

 whilst it is loosely attached to the plantar aspect of the neck 

 of the proximal bone of the joint. The collateral ligaments 

 and the flexor sheath are fixed to its margins, and the trans- 

 verse ligament of the heads of the metatarsal bones is attached 

 to the plantar accessory ligaments of the metacarpo-phalangeal 

 joints. The plantar accessory ligaments always move with the 

 distal bones. 



Ligamenta Collateralia. The collateral ligaments are 

 strong, thick triangular bands placed one on each side of each 

 joint. The apex of the band is attached to the tubercle and 

 the depression on the corresponding side of the head of the 

 proximal bone of the joint, and the expanded base is attached 

 to the side of the base of the distal bone and to the corre- 

 sponding margin of the plantar accessory ligament. 



Movements. It has already been pointed out that at the 

 interphalangeal joints, which are hinge joints, only the move- 

 ments of flexion and extension are permitted, whilst the 



