OF DIDELPHYS VIRGINIANA. 



131 



and anterior to, the long peroneal. It lies at first upon the preceding muscle and extensor 

 of the great toe ; afterwards upon the fibula, alongside the following muscle. Its flattened 

 tendon passes behind the external malleolus, and thence straight to its insertion at the out- 

 side of the base of the fifth metatarsal. 



Peroneus primus s. longus. — (Fig. 33, g, g.) The largest and most superficial of the 

 peroneal group ; a long, flattened spindle, muscular nearly to the ankle. It arises from the 

 outermost part of the head of the fibula, and for a short distance from the shaft of the bone, 

 and from the surrounding intermuscular septa. After passing behind the malleolus its short 

 tendon dips obliquely forward, outward and downward, to gain the side of the foot ; is 

 there reflected around the cuboid, passes through a deep groove (converted by ligament 

 into a sheath) in the under surface of the latter, runs obliquely across the sole, along the 

 bases of the conjoined metatarsals, and is inserted into the outer side of the base of the 

 first metatarsal. Opposite the base of the fifth metatarsal it gives off a short slip to be 

 there inserted. It has the usual action, flexing and elevating the 

 side of the tarsus, in the former respect cooperating with, in the lat- 

 ter counteracting, the tibialis anticus. The peroneus brevis and 

 extensor longus pollicis assist, respectively, the peroneus longus and 

 the tibialis anticus, in the lateral movements of the ankle joint. 

 These four muscles, and the extensor of the digits, collectively oppose, 

 by flexing the tarsus, all the remaining muscles of the leg.^ 



Gastrocnemius internus. — (Fig. 34, c.) This is entirely distinct 

 from the external gastrocnemius and soleus, having separate insertion 

 as well as origin, and no relation in its course except that of con- 

 tiguity. It has extensive origin by a prismatic, fleshy head from 

 the internal condyle, and greater part of popliteal space of femur, 

 across to the outer condyle. About an inch and a half below the 

 knee it suddenly contracts to a stout, flat tendon, which at the lower 

 third of the leg crosses behind (outside) the tendon of the other 

 gastrocnemius, to be inserted alongside the latter into the outer and 

 lower corner of the tuberosity of the os calcis. 



Gastrocnemius externus and Soleus. — (Fig. 34, a and h, and fig. 

 33, h.) The outer muscular belly of the calf is much larger than 

 the other, and of complex structure, apparently resulting from blend- 

 ing with a soleus. Its three parts are disposed thus: A flattened ^jg, g^^Left leg, posterior 

 ovate or split almond-shaped mass arises from the external condyle, " view; natural size. 



digital extensor. Per contra, however, the human peroneus 

 tertius may be an arrested extensor minimi digiti. 



Again, the extensor of the opossum's little toe may be, 

 morphologically, a part of the fibular muscle that supplies 

 the next thi-ee toes; the two parts, then, together constitut- 

 ing the peroneus tertius. This second mode of viewing the 

 subject leaves us free, as in the first instance, to identify the 

 slip upon the dorsum of the foot as the whole of the flexor 

 brevis digitorum, in a rudimentary condition. 



AVith this explanation I allow the above descriptions to 

 stand just as they were penned at the times of making the 

 dissections. 



iProf. Owen thus describes the peroneal muscles of Dasy- 

 urus 7nrtcr!/r»s (op. cit., p. 16): "There are three peronei: 

 the external one is inserted into the proximal end of the 

 fifth metatarsal; the tendon of the middle peroneus crosses 

 the sole in a groove of the cuboid, like the peroneus longus; 

 the internal peroneus is an extensor of the outer or fifth toe." 

 Of these, the first mentioned, or " external " peroneus, is 

 the one described above as the p. aecundm sQnbrp.vis\ the 

 next, or " middle" peroneus, is the p. pritnus seu longus, of 

 this paper; while the last, or " internal" peroneus is the p. 

 tertius — according to mv identification. 



