REPORT ON THE MARSUPIALIA. 43 



being joined by the tendon of the flexor longus digitorum, it splits into four, viz., a 

 tendon for each toe. 



In the Thylacine a small flexor brevis digitorum is found in the sole of the foot. 1 1 

 lies under cover of the expanded tendon of the plantaris, and springs from the inner 

 aspect of the os calcis close to its posterior extremity. Four delicate tendons issue from 

 it, and these pass downwards for a short distance in a groove on the superficial aspect of 

 the large tendon of the flexor longus hallucis, and then diverge to reach their respective 

 digits. The insertion of the flexor tendons upon the plantar face of the digits is effected 

 in the usual manner. 



We must now look at the arrangement of the huge flexor mass on the posterior aspect 

 of the leg of the Cuscus. It occupies the place of the flexor longus hallucis, and arises 

 from the whole length of the posterior aspect of the fibula as in the Thylacine, and also 

 from the fascia covering the popliteus. About the middle of the leg it divides into two, 

 viz., (1) a small superficial portion (PI. V. fig. 2, e), and (2) a large deep part (PI. V. fig. 2, d). 

 These bear to each other very much the same relation that the flexor sublimis in the fore- 

 arm of the same animal bears to the flexor profundus. The sublimis or superficial part 

 ends in three tendons, and is the representative of the flexor brevis digitoruni. It is 

 interesting to note that it is supplied by a recurrent branch from the internal plantar 

 nerve, whilst the profundus or deeper part is supplied by a twig from the internal popliteal 

 nerve. The profundus ends in a rope-like tendon, which is grooved for the reception of 

 the three delicate tendons of the flexor brevis digitorum. In the sole it divides into five 

 tendons — one for each toe. The three tendons of the flexor brevis digitorum go to the 

 minimus, annularis, and niedius, and are pierced by the deep tendons. 1 



Lumbricales. — In the Cuscus these are four in number, and with the exception of 

 that for the index they are very large, and expand so much towards their insertions that 

 their attachment extends along the whole length of the first phalanx. PI. III. fig. 1 , /. 

 shows the lumbrical of the annular digit. 



In the Thylacine the lumbrical muscles are peculiar. Each muscle is double, so that 

 one arises from each side of the deep flexor tendon and envelopes it completely in sparse 

 muscular fibres. Again, they are not inserted into the dorsal extensor expansion but are 

 attached to the flexor sheaths of the digits — two to each toe. 



Popliteus (pronator tibiae). — This muscle consists of a continuous layer of oblique 

 fibres which occupies the entire interosseous space. It is thick and fleshy in its upper 

 and lower thirds, but its middle third is very thin, and has a large admixture of tendinous 

 fibres entering into its composition. The fibres of the muscle pass from the fibula 

 obliquely downwards and inwards to the tibia. 



In the Cuscus, in which the interspace between the bones is wide and the movenn nt 

 of the fibula peculiarly free, the attachment of the muscle in different planes (so well 

 1 There is no musculus accessoriua in the foot of either Thylacinus or Cuscus. 



