MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES OSGOOD. 53 



beneath it. Its large tendon passes beneath the annular ligament out- 

 side the external malleolus and after passing over the front of the 

 calcaneum turns downward and inserts on the outer side of the tuberos- 

 ity of the base of the fifth metacarpal. Just above its insertion it is 

 distinctly increased in size and is perforated by the tendon of the 

 peroneus tertius. The same arrangement has been noted in Trichosurus 

 (Thompson and Hillier, 1905, p. 322). 



Tibialis anticus. Origin from the deeply excavated outer surface of 

 the proximal part of the tibia. Its muscular part lies mostly in this 

 broad groove but is directly attached to the bone only in its proximal 

 third. Its principal tendon passes along the fibular edge of the tibia 

 and after passing over the astragalus turns down entad of the tendon of 

 the extensor hallucis longus and widening slightly inserts on the under 

 side of the entocuneiform bone. A second and smaller tendon runs from 

 an indistinct division of the fleshy part of the muscle and, paralleling 

 the larger tendon, inserts in front of it on the side of the base of the first 

 metatarsal. 



In Myrmecobius (Leche, Bronn's Thierr., VI, p. 893) it is joined by 

 the tendon of the extensor hallucis longus, but in this case that muscle 

 and its tendon are independently developed. An accessory tendon to 

 the first metatarsal similar to that in C&nolestes was found in Notoryctes 

 by Thompson and Hillier. 



Peroneus tertius. Origin from the external condyle of the femur and 

 the under surface of the collateral ligament jointly with the peroneus 

 longus, from the outer surface of the inner condyle of the fibula and also 

 by a distinct slip or second head from the surface of the fibula just 

 distad of the outer tuberosity. It lies entad of the peroneus longus and 

 although not so completely bicipital there is a distinct correspondence 

 between the divisions of each. It has only slight connection with 

 surrounding muscles, being distinct throughout its fleshy extent. 

 Its tendon passes through the malleolar ligament, perforates the tendon 

 of the peroneus brevis and continues directly to its insertion in the fascia 

 on the outer side of the base of the first phalanx of the fifth digit. 



This muscle is regarded by Leche as a division of the extensor brevis 

 digitorum. Its relations in Didelphis are similar to those in C&nolestes 

 and also in Thylacinus, Myrmecobius, Cuscus, and in Phascolarctos, but 

 in these latter it has no femoral origin (Leche). 



Peroneus longus. Arises by two heads which are separate proximally 

 but which join midway of their fleshy extent to form a single tendon. 

 The inner head lying next to the peroneus brevis takes origin from the 

 inner tuberosity of the fibula and from the outer edge of a collateral liga- 

 ment running from the external condyle of the femur to the inner tuber- 



