THE ARTICULATIONS OF THE FOOT. 



197 



only an indistinct smooth surface covered by synovial membrane (see figs. 152 and 

 154) : this bursa may communicate with the first cuneo-metatarsal joint. 



Transverse metatarsal ligament. The digital extremities or heads of the 

 metatarsai bones are loosely connected by a transverse band, which is identical in its 

 arrangement with the corresponding structure in the hand, with this exception, that 

 it is attached to the great toe, whereas in the hand the transverse metacarpal 

 ligament does not reach the thumb. 



METATARSO-PHALANGEAL AND INTERPHALANGEAL ARTICULATIONS. The heads 

 of the metatarsal bones are connected with the small concave articular surfaces of 

 the first phalanges by two lateral ligaments, an inferior ligament, which is developed 

 into a thick fibrous or sesamoid plate, and a synovial membrane, all being closely 

 similar to the corresponding parts of the hand. In the first metatarso-phalangeal 

 articulation the sesamoid plate is divided into two parts, which are fully ossified, 

 forming the sesamoid bones. These are held together by strong transverse liga- 

 mentous fibres, and being provided with cartilaginous surfaces, move upon the 

 corresponding grooved cartilaginous surfaces of the head of the first metatarsal bone. 



Fig. 224. SAGITTAL SECTION OP THE ANKLE-JOINT AND ARTICULATIONS OP THE RIGHT FOOT, A LITTLE 



TO THE INSIDE OP THE MIDDLE OP THE GREAT TOE. (Allen Thomson. ) i 



1, synovial cavity of the ankle-joint ; 2, posterior astragalo-calcaneal articulation ; 3, 3', astragalo- 

 calcaneo-navicular articulation : the interosseous ligament is seen separating 2 from 3' ; 4, inferior 

 calcaneo-navicular ligament ; 5, part of the long plantar ligament ; 6, naviculo-cuneiform articulation ; 

 7, first cuneo-metatarsal articulation ; 8, first metatarso-phalangeal articulation ; 9, section of the inner 

 sesamoid bone ; 10, interphalangeal articulation ; 11, placed on the calcaneum, indicates the bursa 

 between the upper part of the tuberosity of that bone and the tendo Achillis. 



The articulations of the phalanges with one another are also constructed on the 

 same plan as those of the superior extremity. In each the bones are held in contact 

 by two lateral ligaments and an inferior ligament or fibrous plate ; and each of the 

 cavities is lined by a synovial membrane. 



Mechanism and movements. In the mechanism of the foot a longitudinal and a 

 transverse arch are to be recognized, both of them capable of being flattened somewhat by 

 pressure from above, thus securing elasticity. The longitudinal arch, as analyzed by v. 

 Meyer, is formed primarily by the calcaneum, astragalus, cuboid, navicular, external cunei- 

 form and third metatarsal bones, the external cuneiform being wedged in between the 

 navicular and cuboid, and the third metatarsal being firmly united at its base by strong 

 ligaments, so that very little movement is allowed. To the slender anterior pillar of the 

 arch lateral supports are added, the fourth and fifth metatarsal bones on the outer side, the 

 second and first metatarsal bones on the inner side, which are capable of greater movement, 

 can be adjusted to the form of the supporting surface, and are brought into play according as 

 the weight is thrown on the one or the other side of the foot. The first metatarsal bone and 

 the great toe have their chief use in progression. In making a step, as the heel of the 



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