THE METATARSAL JOINTS. 447 



The second tarso-metatarsal joint opens at the inner side into the great 

 tarsal joint, and usually with that of the external cuneiform and third metatarsal. 

 The motions of these joints are slight and 

 indefinite. • ^'g. 462. 



The fourth and fifth tarso-metatarsal Head of first metatarsal 



joints, between the cuboid and the two outer 

 metatarsal bones, are nearly or quite separated ^ . , 



f I 1- I i'-^ ^1- Synovial- 



from the precedmg by the mterosseous hga- cavity 



ment from between the outer cuneiform and 



the cuboid to the third and fourth metatarsals ; internai-T^----"!?^;'^;'":-'*W 



practically they form a distinct joint. The sesamoid bone %j^^^^^se^mo[d1)one 



motion is much more free than in the others. ^lont*^,'!: hi I'w?!''^^^^ 



^, r ., , ^ , , 1 ^u 4-U- J longub hallucis Glenoid ligament 



1 he fourth metatarsal bone plays on the third 



1 r^j'i .1- 1- ^ Transverse section through head of first meta- 



by a facet distal to tne interosseous ligament tarsal bone. 



just mentioned. The fifth plays still more 



freely both on the fourth and on the cuboid. The motion is of a nature to permit 



the drawing of the outer side of the foot downward and inward so as to deepen the 



hollow of the sole. It also allows the outer metatarsals to be displaced dorsally 



when the transverse arch is flattened. 



THE METATARSO-PHALANGEAL JOINTS. 



These articulations in the foot are similar to the corresponding ones of the hand, 

 the capsule including the glenoid and lateral ligaments ; the latter arise from both 

 the tubercles and the depressions on the heads of the metatarsals. That of the great 

 toe is large and distinguished by the large size of the sesamoid bones, which are 

 interposed between the head of the metatarsal and the ground. As in the hand, there 

 is no glenoid ligament in this joint. The transverse metatarsal ligament differs from 

 that of the hand in connecting all the toes. The motions correspond to those of 

 the hand, but the range of dorsal extension is greater. Lateral motion is possible 

 only when the toes are nearly straight. 



The structure and motions of the interphalangeal joints are as in the hand. 



SYNOVIAL CAVITIES. 



The following synovial cavities are found (Figs. 458, 463). (i) That of the 

 ankle-joint proper ; (2) \.he posterior calcaneo-astragaloid ; (3) the anterior ealcafieo- 

 astragaloid completed by .the scaphoid ; (4) the calcaneo-ciiboid ; (5) the scapho- 

 cuneiform cuboid, the great tarsal cavity which communicates with the joints at the 

 bases of the second and third metatarsals by a passage at the inner side of the middle 

 cuneiform and sometimes by one on its outer side. This may also open into the 

 preceding synovial cavity ; (6) the joint between the inter?ial cuneiform and the 

 Jirst metatarsal ; (7) that of the ciiboid and the ojiter two metatarsals . 



The arrangement of the synovial sacs about the bases of the second and third 

 metatarsals is variable. 



THE FOOT AS A WHOLE. 



The foot is a vault which may be considered as composed of an indefinite number 

 of arches diverging from the internal tuberosity of the calcaneum and ending in 

 front at the heads "of the metatarsals. The highest arch is that in the line of the 

 great toe, a fact in some degree due to the sesamoid bones which are between the head 

 of the first metatarsal and the ground. The arch at the outer side of the foot is the 

 lowest. It is clear from this conception that transverse sections of the foot must 

 also show an arched structure the details of which must vary with the line of section. 

 The shape of the three cuneiforms is an essential element in this construction. This 

 vault is, however, not rigid, but elastic and capable of considerable modification of 

 shape under varying pressure. 



In the motions of the foot the essential joints below the ankle are the subastraga- 

 loid and those between the astragalus and the scaphoid and the calcaneum and the 

 cuboid. 



