THE PLANTAR MUSCLES OF THE FOOT 495 



The Fourth Layer. 

 Interossei. 



The Interossei in the foot are similar to those in the hand, with this exception, 

 that they are grouped around the middle line of the second digit, instead of that 

 of the third. They are seven in number, and consist of two groups, dorsal and 

 plantar. 



The Interossei dorsales (Dorsal interossei) (Fig. 446), /owr in number, are situated 

 between the metatarsal bones. They are bipenniform muscles, each arising by 

 two heads from the adjacent sides of the metatarsal bones between which it is 

 placed ; their tendons are inserted into the bases of the first phalanges, and into the 

 aponeurosis of the tendons of the Extensor digitomm longus. In the angular 

 interval left between the heads of each of the three lateral muscles, one of the 

 perforating arteries passes to the dorsum of the foot; through the space between 

 the heads of the first muscle the deep plantar branch of the dorsalis pedis artery 

 enters the sole of the foot. The first is inserted into the medial side of the second 

 toe; the other three are inserted into the lateral sides of the second, third, and 

 fourth toes. 



FIG. 446. The Interossei dorsales. Left foot. 



Fio. 447. -The Interossei plantares. Left foot. 



The Interossei plantares (Plantar interossei) (Fig. 447), three in number, lie 

 beneath rather than between the metatarsal bones, and each is connected with 

 but one metatarsal bone. They arise from the bases and medial sides of the bodies 

 of the third, fourth, and fifth metatarsal bones, and are inserted into the medial 

 sides of the bases of the first phalanges of the same toes, and into the aponeuroses 

 of the tendons of the Extensor digitorum longus. 



Nerves. The Flexor digitorum brevis, the Flexor hallucis brevis, the Abductor hallucis, 

 and the first Lumbricalis are supplied by the medial plantar nerve; all the other muscles in the 

 sole of the foot by the lateral plantar. The first Interosseous dorsalis frequently receives an 

 extra filament from the medial branch of the deep peroneal nerve on the dorsum of the foot, 

 and the second Interosseous dorsalis a twig from the lateral branch of the same nerve. 



Actions. All the muscles of the' foot act upon the toes, and may be grouped as abductors, 

 adductors, flexors, or extensors. The abductors are the Interossei dorsales, the Abductor hallucis, 





