390 PRACTICAL ANATOMY. 



way of the tendon. (Fig. 268.) Now cut all three of these muscles and turn 

 them forward, and expose the second layer of muscles. (Fig. 270.) Having 

 cut through the ligamenta vaginales of the toes (Fig. 272), observe that the 

 four tendons of the flexor longus digitorum pass through slits in the four 

 corresponding tendons of the flexor brevis digitorum, in the same manner the 

 deep flexors of the fingers pass through the superficial ones. 



Second Layer (Fig. 270). In the figure of the flexor longus digitorum 

 notice three accessories: (i) The muscular acccssorius (Fig. 268) ; (2) the four 

 limibricales (Fig. 273); (3) a slip of contribution from the tendon of tlie flexor 

 longus Iiallueis. (Fig. 270.) Having studied the origin and insertion of these 

 muscles, divide the flexor longus hallucis and flexor longus digitorum near the 

 os calcis and turn them all forward, as you did the previous layer. 



Third Layer (Fig. 274). Trace out to its origin each one of the three mus- 

 cles inserted into the base of the great toe. Cut down between the two sesamoid 

 bones in the tendon of the flexor brevis hallucis. Trace the tendon of the 

 peroneus longus across the sole of the foot to its insertion into the internal cunei- 

 form and base of great toe metatarsal. (Fig. 275.) 



In the fourth layer we have the dorsal interossei and the plantar interossei. 

 In number they are seven, four being dorsal and three plantar. In action they 

 are analogous to the interossei of the hand. In the foot they are all supplied 

 by the external plantar nerve ; in the hand by the ulnar nerve. 



Function of the Interossei and Lumbricales. It is comprehensive to consider 

 the action of these muscles in this manner in the hand : 



1. All the interossei and lumbricales acting together, flex at the metacarpo- 

 phalangeal articulation and extend at the first and second phalangeal articula- 

 tions. This gives about the position for'holding the pen. 



2. The four dorsal interossei acting alone, abduct the digits. Notice that 

 supination of the forearm is involuntarily associated with abduction of the 

 digits. 



3. The palmar interossei acting alone, adduct the digits. Notice that prona- 

 tion of the forearm is associated involuntarily with adduction of the fingers. In 

 the above I have described the action of these muscles in the hand ; the action 

 in the foot is the same, only less under control of the will, since the foot of man 

 is not a prehensile member. 



4. The adductor line of fingers and toes. The adductor finger is the 

 middle ; the adductor toe is the second. In adduction and abduction the other 

 digits approach and recede from this adductor digit. 



The Adductor Digit. (i) The adductor digit of the hand has no palmar 

 interossei inserted into it ; (2) the adductor digit of hand has two dorsal inter- 

 ossei inserted into it ; the same is true of the foot. 



Difference in Origin. Notice that the dorsal interossei are very large, and 

 arise from the contiguous sides of the metatarsals or metacarpals ; that the 

 palmar are small, and arise from one side only of the metatarsal or metacarpal 

 corresponding to the phalanx into which they are inserted. Practise the 

 movements of the lumbricales and interossei on your own fingers until you 

 master this subject thoroughly. 



Granular Fat. Found in the superficial fascia of the hand and foot palmar 

 and plantar surfaces and in the general supi-rficial fascia of the f(utus and infant. 

 Tin- toughness of this kind of fatty tissue depends on a largi r amount of con- 

 nective tissue. 



Divisions of Plantar Fascia. (i) An outer thin one that covers the ab- 

 ductor minimi digiti. (2) An inner one that covers the abductor Jiallneis. (3) A 

 middle one that covers the flexor bre:<is digitorum. This middle one is very 

 strong. 



