REPORT ON THE MARSUPIALIA. 41 



no fibres from the popliteal surface of the femur. Half-way down the leg, it gives place to 

 a narrow tendon which has an independent insertion into the back of the os calcis (b'). The 

 outer head has the same origin as in the Thylacine, with two exceptions, viz., (1) it has no 

 tendinous slip attached to the outer aspect of the external condyle of the femur, and (2) 

 it springs from the posterior aspect of the fibula in its upper two thirds through the 

 medium of the intermuscular septum which intervenes between it and the peronei 

 muscles. It is inserted by a strong tendon into the tuber of the os calcis, under cover of 

 the tendon of the inner head (a 1 ). 



The fibular origin of the outer head of the gastrocnemius points very clearly to the 

 fact that it is a compound muscle, and contains in its midst the fibres of the absent 

 soleus. That the plantaris lies under cover of this muscle, is no proof against this 

 view, and is certainly not evidence sufficient to lead one to look for the lost soleus 

 amongst the deep muscles of the calf. 1 The plantaris is subjacent only to the inner part 

 of the compound muscle, and does not lie under cover of the outer part which represents 

 the soleus (PL V. fig. 2, e). 



Plantaris. — In Thylacinus this muscle arises in common with the outer head of the 

 gastrocnemius, and remains fused with its under surface for a considerable distance. It 

 ends in a strong tendon which proceeds downwards along the inner side of the tendo 

 achillis to the heel, where it expands, and, passing superficially to the tendo achillis, enters 

 the sole. Here it spreads out in the form of a plantar fascia, which divides into three 

 slips for the index, medius, and annularis. The plantar fascia is not attached to the 

 subjacent muscles, and each of its terminal slips bifurcates to embrace the meta- 

 tarso-phalangeal joint, and is attached to the ligamentous structures around this 

 articulation. 



In the Cuscus (PI. V. fig. 2, c) the plantaris is a large muscle quite distinct from the 

 soleo-gastrocnemius, although it lies under cover of its inner part. It arises from the 

 sesamoid bone attached to the head of the fibula, and, passing over the tuber of the 

 os calcis, it is inserted into a plate of cartilage in the sole which replaces the plantar fascia, 

 and takes the place of the true heel. 



This plantar cartilage (PL VI. fig. 5, p.c.) possesses very definite relations. Inter- 

 nally it is attached to a sesamoid bone which glides upon the internal cuneiform, and 

 wives attachment to some of the short muscles of the hallux ; externally it is fixed to the 

 under surface of the cuboid, and here it gives origin to some of the short muscles of the 

 minimus; posteriorly the plantaris tendon (p.t.) is inserted into it; whilst in front it is 

 prolonged forward in the form of fascial slips, to the roots of the digits. 



The plantaris is almost invariably present amongst the Marsupials. It is absent 

 however in the Wombat." 



1 Young, Muscular Anatomy of the Koala, p. 237, Jour. Anat. and Phys., vol. xvi. 



2 Macalister, loc. cit., p. 3. 



(ZOOL. CHALL. EXP. — PART XVI. 1882.) Q 6 



