310 THE ARTICULATIONS 



of fibres passing transversely from bone to bone, blending with the fibro-cartilagi- 

 nous or sesamoid plates of the metatarso-phalangeal joints, and the sheaths of the 

 flexor tendons where they are connected with the fibro-cartiUiges. It differs 

 from the corresponding Hgament in the hand by having a band from the first to 

 the second metatarsal bone. 



8. THE METATARSO-PHALANGEAL ARTICULATIONS 



(a) The Metataeso-phalangeal Joints of the Four Lateral Toes 



Class. — Diarthrosis. Subdivision. — Condylarthrosis. 



These joints are formed by the concave proximal ends of the first phalanges 

 articulating with the rounded heads of the metatarsal bones, and united by 

 articular capsules strengthened by the following ligaments: — ■ 



Collateral. Dorsal. Plantar accessory. 



The two collateral ligaments are strong bands passing fi-om a ridge on each side of the head 

 of the metatarsal bone to the sides of the proximal end of the first phalanx, and also to the sides 

 of the sesamoid plate which unites the two bones on their plantar surfaces. On the dorsal 

 aspect they are united by the dorsal ligament. 



The dorsal ligament consists of loose fine fibres of areolo-fibrous tissue, extending between 

 the collateral ligaments, thus completing a capsule. It is connected by fine fibres to the under 

 surface of the extensor tendons, which pass over and considerably strengthen this portion of the 

 capsule. 



The plantar accessory ligament or sesamoid plate helps to deepen the shallow facet of the 

 phalanx for the head of the metatarsal bone, and corresponds to the accessory volar ligament of 

 the fingers. It is firmly connected to the collateral ligaments and the transverse ligament, and 

 is grooved interiorly where the flexor tendons pass over it. It serves to prevent dorsal disloca- 

 tion of the phalanx. 



The second metatarso-phalangeal joint is 6 mm. {\ in.) in front of both the first and third 

 metatarso-phalangeal joints. 



The third metatarso-phalangeal joint is 6 mm. (i in.) in front of the fourth, and the fourth. 

 9 mm. (f in.) in front of the fifth. 



The head of the fifth metatarsal is in line with the neck of the fourth. 



Thus the lateral side of the longitudinal arch of the foot is shorter than the medial, it is 

 also distinctly shallower. 



(6) The Metatarso-phalangeal Joint of the Great Toe 



The metatarso-phalangeal joint of the great toe differs from the rest in the 

 following particulars : — 



(1) The bones are on a larger scale, and the articular surfaces are more extensive. 



(2) There are two grooves on the plantar surface of the metatarsal bone, one on each side 

 of the median line, for the sesamoid bones. 



(3) The sesamoid bones replace the accessory plantar ligament (sesamoid plate). They 

 are two small hemispherical bones developed in the tendons of the flexor hallucis brevis, convex 

 below, but flat above where they play in grooves on the head of the metatarsal bone; they are 

 united V)y a strong transverse ligamentous band, which is smooth below and forms part of the 

 channel along which the long flexor tendon plays. They are firmly united to the base of the 

 I)halanx by strong short fibres, but to the metatarsal bone they are joined by somewhat looser 

 fibres. At the sides th(!y are connected with the collateral ligaments and the sheath of the flexor 

 tendon. They provide shifting leverage for the flexor hallucis brevis as well as for the flexor 

 hallucis longus. 



The arteries come from the digital and metatarsal branches; and the nerves from the cuta- 

 neous digital, or fi-om small twigs of the nerves to the iiiterossei muscles. 



The movements p(u-mitted are: flexion, extension, abduction, adduction, and circumduction. 



Flexion is more free; than extension, and is limited by the extensor tendons and dorsal liga- 

 ments; exteri.sion is limited by the flexor tendons, the plantar fibres of the collateral ligaments, 

 and the sesamoid j)lates. The side-to-side motion is possible from the shape of the bony surfaces, 

 but is very limited, being most marked in the great toe. It is limited by the collateral ligaments 

 and sesamoid plates. 



9. ^rilK IN^n-^HPIIALANCJEAL JOINTS 



Class. — DidiUirofiifi. Subdivision. — Gtnglymus. 



The articulations between the first and second and second and third phalanges 

 of the toes are similar to those of the fingers, with this important difference, that 



