42 — Mr. W. S. Macrzrax on the Comparative Anatomy 
merely as a group connecting the Fere 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 Gres... 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 prés qu'ils ne tiennent aux autres êtres, ils s'en 
trouvent neanmoins qui font des pointes au dehors, et semblent 
sélancer pour atteindre à 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, ofall. 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 
otherfingers. Birds have but one exterior opening for the in- 
testinal canal and the organs of generation :—-no more has the 
- * Hist. Nat. tom. xiii. p. 330, ed. 4,5 — ck: Herm. Tab. Aff. Anim. p. 117. 
I Cuv. Règne Anim. i. 204. & Herm. Tab. Aff. Anim. p.118. 
Beaver. 
