278 Bulletin American Museum of Natural History. [Vol. XXVII, 



The astragalus of Tupata is of especial interest because on the whole, 

 it resembles the Primate types and contrasts with those of all the Lipotyphla 

 in important details. As in the lemurs the trochlea is narrow above (proxi- 

 mally) and broader below, the inner or tibial crest less prominent than the 

 outer or fibular crest and the trochlear concavity very slight; the trochlea 

 also extends postero-dorsally above the ectal or calcaneal facet. The malleo- 

 lar facets are sub vertical and that on the tibial side extends anteroinferiorly 

 below the trochlea. The head (navicular facet) is very ovoid and extends 

 well up on the antero-external corner. In the back view also the resemblances 

 to the lemuroids are numerous. The ectal facet is obliquely extended and 

 the rather long sustentacular facet is broadly continuous below with the 

 navicular facet; whereas in the Lipotyphla the ectal facet is usually subtrian- 

 gular and the oval sustentacular is separated from the navicular facet. The 

 calcaneum as in other plantigrade and arboreal mammals has a very short 

 tuber. 



Dissection of an alcoholic specimen of Tupaia sp. shows that the lemuroid 

 characters of the tarsus may be related to arboreal habits, e. g. the strong 

 internal and external malleoli, with their vertical facets on the astragalus, 

 evidently serve to prevent lateral dislocation and to limit the motion of the 

 astragalus upon the tibia to the fore and aft plane; the dorsal continuation 

 of the trochlea permits extreme extension of the foot upon the tibia, the long 

 oblique neck and oval head may permit the sole to be turned inward as in 

 climbing, the short tuber calcis enables the foot to be extended very suddenly 

 and is thus of advantage in leaping. 



Adaptive Contrasts between Tupaia and Solenodon. 



The foregoing descriptions of Solenodon (pp. 253-255) and Tupaia (pp. 

 272-278) offer some instructive contrasts when considered in connection with 

 the diverse habits of the two forms. In Solenodon all the skeletal adaptations, 

 such as the very powerful limbs, plantigrade feet, heavy claws, arched back 

 and very stout tail, indicate a slow- moving type analogous to Orycteropiis. 

 In Tupaia the skull and skeleton express with equal clearness the animal's 

 arboreal habits, quick senses and great agility. It is very probable that the 

 arboreal type of skeleton represented in Tupaia is on the whole more primi- 

 tive (except as to the large brain case, and other features) than the terrestrial, 

 semifossorial type represented by Solenodon; partly because the latter is 

 distinguished by certain specializations, such as the loss of divergence of the 

 poUex and hallux, the development of very strong trochlear ridges on the 

 astragalus, the incipient coalescence of the tibia and fibula, the loss of 

 lumbar parapophyses etc. 



