MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 59 



where they arise. This sesamoid may not be homologous with that of 

 Notoryctes, but it is otherwise unique among marsupials and, as noted 

 by Thompson and Hillier, 1 is suggestive of certain edentates. The 

 flexors of the fifth digit are separated at their insertion by the tendon of 

 the shorter division of the abductor minimi digiti. It is somewhat doubt- 

 ful as to whether the outer or radial division is properly to be regarded 

 as a flexor, especially since it inserts by a slender tendon whereas its 

 fellow has a broad fleshy insertion extending to both sesamoids. Pos- 

 sibly this supposed outer division of the fifth flexor should be regarded 

 as a third division of the abductor minimi digiti. 



SUMMARY OF MYOLOGICAL CHARACTERS. 



The trunk muscles of Canolestes are, as was to be expected, of the 

 prevailing marsupial type. It is in the muscles of the limbs and head that 

 the most significant deviations are found and although these seem quite 

 numerous when comparison is made only with American forms, there is 

 such variation among Australian forms that similarity is found with first 

 one and then another. It is quite evident that some Australian forms, 

 especially in the Dasyuridae, approach Didelphis more closely than does 

 C&nolestes. It is also clear that many of the points in which C&nolestes 

 differs from Didelphis are to be found in Australian forms. Although 

 some of these resemblances are plainly cases of convergence, others do 

 not seem so. Therefore, aside from the question as to the nearest re- 

 lationships of C&nolestes, it is evident that it contributes in a positive 

 way to the broad general conclusion, already well grounded, that Ameri- 

 can and Australian marsupials are of common derivation. That is, 

 many of the points in which Didelphis fails to show resemblance to 

 Australian forms are supplied by Ccenolestes. 



From the standpoint of myology there seem to be few if any distinc- 

 tions that can be definitely drawn between Polyprotodontia and 

 Diprotodontia. Nevertheless, in viewing the possibility that C&nolestes 

 is to some extent transitional between the two large groups, the muscula- 

 ture can scarcely be adduced as contrary evidence, since it shares many 

 features with the diprotodonts that are not possessed by all polypro- 

 todonts. That it shares more than any polyprotodont cannot be said, 



Regarding the sesamoid in Notoryctes, these authors say: "In connection with 

 the plantar sesamoid bone, which as far as we know has not been recorded in any 

 other marsupial, it is interesting to find that in some edentates there is a very similar 

 arrangement. Windle and Parsons state that in the Dasypodidae the tibial and 

 fibular flexors unite in the lower part of the leg, and are inserted into a very large 

 sesamoid bone in the sole of the foot, which is held in place by a fibrous band from 

 the calcaneum, the equivalent of the accessorius. From the front of the sesamoid 

 bone five tendons pass to the terminal phalanges of the five digits." Jour. Anat. & 

 Phys., XXXIX, p. 326, 1905. 



