534 



THE MUSCLES AND FASCIA. 



Fourth Layer. 

 The Interossei. 



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

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

 of the middle line of the third finger, as in the hand. They are seven in number, 

 and consist of two groups, dorsal and plantar. 



The Dorsal interossei, four in number, are situated between the metatarsal 

 bones. They are bipenniform muscles, arising by two heads from the adjacent 

 sides of the metatarsal bones, between which they are placed ; their tendons are 

 inserted into the bases of the first phalanges, and into the aponeurosis of the 

 common extensor tendon. In the angular interval left between the heads of 



FIG. 336. The Dorsal interossei. Left foot. 



FIG. 337. The Plantar interossei. Left foot. 



each muscle at its posterior extremity the perforating arteries pass to the 

 dorsum of the foot, except in the First interosseous muscle, where the interval 

 allows the passage of the communicating branch of the dorsalis pedis artery. 

 The First dorsal interosseous muscle is inserted into the inner side of the second 

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

 fourth toes. 



The Plantar interossei, three in number, lie beneath, rather than between, the 

 metatarsal bones. They are single muscles, and are each connected with but one 

 metatarsal bone. They arise from the base and inner sides of the shaft of the 

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

 the bases of the first phalanges of the same toes, and into the aponeurosis of the 

 common extensor tendon. 



Nerves. The Flexor brevis digitorum, the Flexor brevis and ^ Abductor 

 hallucis, and the two inner Lumbricales are supplied by the internal plantar 

 nerve ; all the other muscles in the sole of the foot by the external plantar. The 

 First and Second dorsal interossei muscles receive extra filaments from the gan- 

 glionic enlargement of the anterior tibial nerve on the dorsum of the foot. 



Actions. All the muscles of the foot act upon the toes, and for purposes of 

 description as regards their action may be grouped as Abductors, Adductors, 



