IXTEROSSEI 385 



phalanx of the httle toe; (2) the outer part of tlie front of the under surface of 

 the til'th metatarsal l)one. 



Structure. — Arising tendinous, the fleshy filjres run forwards and a little out- 

 Avards to their short tendon of insertion, which is closely l)lended with that of the 

 abductor minimi digiti. A few of the deeper fibres end in the metatarsal bone. 



Nerve-supply. — From the external plantar nerve by a branch which enters the 

 under surface of the muscle. 



Action. — To flex and slightly abduct the first phalanx of the little toe. 



Relations. — Superficially, the flexor longus digitorum and abductor minimi 

 digiti; deeply, the interossei of the outermost interspace. 



Variations. — The in.sertion upon the metatarsal bone may form a sej^arate muscle, tlie 

 opponeus digiti pedis quiuti, or it maj' be entirely absent. 



Fourth Layer 



The fourth layer consists of the seven interosseous muscles. 



IXTEROSSEI 



The interossei — named from their position between the metatarsal bones — are, 

 like those of the hand, seven in number, three being plantar and four dorsal. 

 The plantar are small and narrow fusiform bundles; the dorsal are bipenniform 

 and of a somewhat Ijroader fusifomi shape than the plantar. The interossei of the 

 foot differ from those of the hand in the fact that they adduct and abduct with respect 

 to a longitudinal axis through the line of the second toe; whereas in the hand the 

 median line passes through the middle finger. 



The plantar interossei. — Origin. — (1 ) The inner and lower surfaces of the three 

 outer metatarsal bones; (2; the adjacent part of the sheath of the peroneus longus 

 tendon. 



Insertion. — (1) The inner side of the bases of the first phalanges of the three 

 outer toes; ( 2) the inner ])order of the expansions of the long extensor tendons on 

 the back of the first |)halanges of the same toes. 



The dorsal interossei arise from the adjacent surfaces of the metatarsal bones 

 bounding each interosseous space. The first dorsal interosseous, however, differs 

 somewhat in its internal head, which is from the base only of the first metatarsal 

 bone and the adjacent outer surface of the internal cuneiform bone. 



Insertion. — The first dorsal interosseous is inserted into: — (1) the inner side of 

 the base of the first phalanx of the second toe; (2) the inner edge of the aponeurosis 

 of the extensor tendon upon the back of the first phalanx. The second, third, and 

 fourth are inserted respectively into: — CI) the outer sides of the bases of the first 

 phalanges of the second, third, and fourth toes; (2) the outer borders of the extensor 

 tendons upon the backs of the same phalanges. 



Structure. — The plantar interossei are penniform muscles consisting of fleshy 

 fil)res which run forwards to the outer side of a tendon which begins about the 

 middle of the space and becomes free opposite the heads of the metatarsal bones. 



The dorsal interossei are bipenniform, and consist of fleshy fibres which con- 

 verge from both sides of the space upon a central tendon Avhich begins about the 

 middle of the interosseous space and becomes free opposite the heads of the meta- 

 tarsal bones. The tendons of both sets of muscles before their insertion lie al)ove 

 the deep transverse metatarsal ligament which separates them from the tendons 

 of the luml)ricales. On the dor.«um of the foot the dorsal interossei are alone 

 visil)lo; in the sole of the foot both sets are seen. 



Nerve-supply. — From the external plantar nerve by filaments which enter the 

 }ilantar aspect of the muscles, somewhat behind the middle of the interosseous 

 space. 



Action. — The common action of all the interossei is (1) to flex the first 

 phalanges of the four outer toes; (2) to extend the second and third phalanges. In 

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