MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 51 



longus. It lies against the lateral head with various nerves intervening 

 and is joined with it in the distal fourth of its fleshy extent. It thus agrees 

 with most marsupials and differs from Didelphis in which it is wholly 

 free from the lateral head. The lateral head has two divisions, one of 

 which probably represents the soleus. These are: 



1. The principal part arises from the extremity of the fibular sesa- 

 moid opposite the end of the collateral tibial ligament and joins the 

 second part about midway of its fleshy extent. Except for a small tri- 

 angular area along its outer proximal edge where the second part is 

 visible beneath the fascia, it overlies the second part. 



2. The second part arises from the caudal surface of the fabella and 

 from the tendinous edge of the plantaris for about two-fifths of the 

 fleshy extent of the plantaris. It joins the outer part about midway of 

 its fleshy extent. This second and more deep-seated part of the muscle 

 may be the soleus which is not otherwise evident. The conjoined parts 

 form a rounded tendon which runs to an insertion on the calcaneum. 

 As a whole the gastrocnemius forms a deep belly on the leg curving 

 rather abruptly inward to its tendon and occupying in its fleshy part 

 only forty per cent of the length of the leg, the remainder being tendinous. 

 Its outer or anterior edge is continuous with the fascia lata which ex- 

 tends to the patellar region and down the leg entad of and intimately 

 associated with the fascia of the biceps fenwris. In one specimen a 

 slight cleft in this outer edge was observed separating a thin slip which 

 may represent a third or patellar division of the gastrocnemius. 



Plantaris. Origin from the side of the fabella, mediad of the second 

 division of the lateral head of the gastrocnemius and more or less united 

 with it. It continues joined with the gastrocnemius for about two-fifths 

 of its fleshy extent and then becomes free as a slender bundle which 

 proceeds distad covered by the gastrocnemius. Its slender tendon, which 

 at first is entad of that of the gastrocnemius, curves around it and passes 

 over the calcaneum ectad of the gastrocnemius tendon and widens to 

 merge into the plantar fascia where its prolongations could not be traced. 



Flexor digitorumfibularis. This has two divisions scarcely separable 

 in their fleshy part. The smaller one, which is on the tibial side, sends 

 a small tendon beneath the larger one but separate from it until just 

 before it passes the os calcis when the two merge. The fleshy part of the 

 muscle is relatively large, lying next below the gastrocnemius and taking 

 origin from the greater part of the inner and posterior aspects of the 

 fibula from the inner side of the outer tuberosity distad not only in the 

 grooved inner expanded part but also on the proximal part of the rounded 

 posterior aspect. Proximally it is connected by septa with the tibialis 

 anticus and distally some of its fibers arise from the interosseous mem- 



