42 Mr. W. S. Macleay 07i the Comparative Anatomy 



merel}'^ as a group connecting the Fera and Glires by the affi- 

 nity of transultation. A Petaurus approaches closely to a Pte- 

 romys. In the inquiry, therefore, as to the order of Mammalia 

 which approaches most nearly to Birds, we have only to con- 

 sider the Cheiroptera and genus Pteromys. It is clear, that any 

 animal supporting itself in the air so well as a Bat does by means 

 of wings, must not only have strong pectoral muscles, but a 

 crista to the sternum for their attachment. Herein consists all 

 the analogy which the Bat bears to the Bird. Here ends all 

 connection between them ; and the rest of the order to which 

 the Bat belongs have nothing in common with Birds. Let us 

 turn therefore to the Glires. On looking at this order, we per- 

 ceive that here, at least, a remark made by BufFon holds per- 

 fectly true. " Quoique tous les Animaux Quadrupedes tiennent 

 entr'eux de plus pres qu'ils ne tiennent aux autres ^tres, ils s'en 

 trouvent neanmoins qui font des pointes au dehors, et semblent 

 s'61ancer pour atteindre k d'autres classes de la nature* :" 

 Now, although the Pteromys or Flying Squirrel is perhaps, 

 with respect to powers of flight, not so much of a Bird as a 

 Bat, the order of Glires, to which it belongs, makes several 

 attempts as it were to attain the structure of the class of Birds. 

 Indeed, of all Mammalia, we find in this order the greatest 

 number of concordances with Birds ; so that if we cannot spe- 

 cify any particular genus as nearest, we can on the other hand 

 say, that the whole order comes nearest to that class. Dipus 

 gives us the legs and feet of a Birdt; Sciurus, the feathers |.; 

 Hystrix the quills §; and Pteromys, the wings of a Bird. In 

 Cheiromys the thumb is, as generally in birds, opposed to the 

 other fingers. Birds have but one exterior opening for the in- 

 testinal canal and the organs of generation : — no more has the 



* Hist. Nat. torn. xiii. p. 330. ed. 4. t Herm. Tab. Jf. Anim. p. 1 17. 



X Cuv. R^gne Anim. i. 204. § Herm. Tab. Aff. Anim. p. 118. 



Beaver. 



