J. Playfair McMiirricli 



53 



the strong aponcnrosis which passes backwards from the outer border 

 of the pateHa. Thronghont the greater portion of its extent it is barely 

 separable from the gastrocnemius lateralis (Figs. 9 and 10), but below 

 it becomes tendinous and lies below (i. e., anterior to) and to the inner 

 side of the tendon of the gastrocnemius lateralis, from which, however, 

 It is quite distinct. At the ankle joint it lies to the medial side but 

 posterior to the gastrocnemius and soleus tendon and spreads out into 

 the thin but dense plantar aponeurosis. This covers the insertion of 

 the tendo Achillis or its representatives and passes downward over the 

 tuberosity of the os calcis, being attached to the outer surface of that 

 bone by its outer border, but its inner border and the greater part of its 

 central portion is free. Passing on into the foot it gives rise upon its 

 deeper surface to the flexor brevis minimi digiti and may be continued 

 onward as a series of fascial slips to the bases of the digits. 



Fig. 10. — Transverse section through the upper part of the crus of the Mouse. 

 F, fibula ; FF, flexor fibularis ; ^, nerve to flexor fibularls ; Oe, gastrocnemius lateralis ; 

 Gi, gastrocnemius medialis ; P, popliteus; PI, plantaris ; pt, posterior tibial nerve; 

 r'p, ramus profundus ; 8, soleus ; T, tibia ; TP, tibialis posticus. 



The important point about the muscle, so far as its insertion is con- 

 cerned, is its connection with the plantar fascia. That this is its true 

 termination becomes evident in those forms such as Cuscus (Cunning- 

 ham, 8i) in which a plate of cartilage is developed in the fascia, the 

 plantaris being inserted into the proximal border of this cartilage. To 

 describe the plantaris as being continuous with the flexor brevis digi- 

 torum, as is sometimes done, merely leads to confusion; this muscle 

 really arises from the plantar aponeurosis and the slips which extend 

 to the bases of the digits are also portions of the plantar aponeurosis 

 and have no primary relation to the plantaris. 



The soleus, unlike the plantaris is not always distinguishable in the 

 lower mammals. In both the cat and the mouse (Fig. 11, s) it is a well 

 developed muscle which arises from the posterior surface of the upper 

 part of the fibula (Figs. 9 and 10, s) and descends the leg beneath the 



