MAY, 1921. AMERICAN MARSUPIAL, C^ENOLESTES OSGOOD. 55 



consists of a short flat muscle much involved in fascia and arising chiefly 

 from the dorsal surface of the fibular side of the distal annular ligament 

 and the fascia over the os calcis. Its fleshy fibers scarcely reach beyond 

 the base of the metatarsals and its tendon runs to the fascia on the 

 fibular side of the base of the second metatarsal. Fascial connection 

 with the hallux may include a minute tendon but this was not dis- 

 tinguished. A similar extensor Inallucis brevis is found in Didelphis, but it 

 is lacking in Dasyurus, Thylacinus and Myrmecobius. Its presence in 

 C&nolestes appears to be an exclusive resemblance to Didelphis. It is 

 common, however, in other mammals, as for example, the Dasypodidce 

 among edentates. 



Extensor longus digitorum. The digital extensors lie next to the 

 tibialis anticus and take origin from the outer tuberosity of the tibia, 

 the inner tuberosity of the fibula, and septa joining them to the peroneus 

 brevis. Their origin is more largely from the fibula than the tibia. They 

 are united for no more than the proximal third of their fleshy extent and 

 in the remainder of their length are distinct both as to the distal fleshy 

 parts and the tendons. Passing over the ankle they are bound down in 

 common with the tibialis anticus and the extensor hallucis by a broad 

 annular ligament (ligamentum cruciatum) and also by a short stout 

 annular ligament (ligamentum fundiforme) which serves for the passage 

 only of their four ligaments. The most deep-seated of these extensors is 

 that lying next to the tibialis anticus and its tendon goes to the terminal 

 phalanx of the second digit, the next to the third digit and the others 

 to the fourth and fifth, the tendons passing on the inner side of the second 

 phalangeal joint in each case and thence to the dorsal surfaces of the 

 third phalanges. 



Extensor hallucis longus. Origin from the inner edge of the fibula 

 just distad of the inner tuberosity and thence about one fourth of the 

 way to the junction of the fibula and the tibia. A few fibers also spring 

 from the popliteal fascia. Its thin flat muscular part passes beneath the 

 common digital extensor and the peroneus muscles in a diagonal direc- 

 tion from the head of the fibula to the base of the tibial flexure and thence 

 its tendon passes down the tibia beneath the large annular ligament and 

 inserts on the base of the first phalanx of the hallux. 



Popliteus. Origin from the greater part of the inner surface of the 

 proximal half of the tibia. Proximally it reaches nearly to the inner 

 condyle of the tibia while distally it extends almost to the union of tibia 

 and fibula. Its fibers run diagonally across the interosseous space but 

 do not reach the fibula except proximally. Distally the fibers reach not 

 more than half way across the interosseous membrane to which they are 

 attached as a thin nearly transparent sheet. Proximally the muscle has 



