64 DENNIS, ON THE MICROSCOPIC 



comparative anatomist^ to do entire justice to the subject. 

 All I can hope to do is to pioneer the way, and furnish fresh 

 data from which science hereafter may perhaps di'aw her 

 unerring deductions. My present object is to prove, from a 

 general exposition of the structiire of birds, that they had 

 representatives on this planet when the Stonesfield Slate 

 was still the soft mud of a large estuary ; and I purpose, for 

 the thorough elucidation of the question, not only to con- 

 sider the structure of birds, but also of those mammifers 

 and saurians which more or less approach birds in their 

 power of flight, for they are intimately (especially the Ptero- 

 dactyle) connected with the subject. Amongst mammifers, 

 the bats alone have the power of maintaining a continued 

 flight, by the rapid vibrations of membranous Avings, which 

 are in fact but a modification of the arm and hand, so 

 adapted as to enable them to extend a thin canvas by which 

 their bodies are conveyed through the air. To this end the 

 fingers are greatly increased in length, as well as the humerus 

 and radius; the scapula also is large, and lengthened in a 

 slanting direction at its lower portion, for the better attach- 

 ment of muscular power, and to afford greater support to the 

 stroke of the wing ; the clavicles are curved like the furcula 

 of the bird, and perform the united functions of the furcula 

 and coracoids, preventing the compression of the chest and 

 keeping the humerus in its place when acted upon by the 

 pectoral muscles. It must, however, be borne in mind, that 

 there is no deviation in this flying mammal from the plan 

 Natiu"e has laid down in the construction of mammifers ; 

 the bat, because it flies, is not a bird, no more than the bird 

 that swims and cannot fly is a fish. If you examine the fin 

 of the penguin, you will observe the same plan of construc- 

 tion that exists in the wing of the eagle ; so the wing of the 

 bat is in accordance with the same design that framed the 

 hand of man. Nature can adapt without confusion, and 

 although, as Cuvier says, the bats seem to have the appear- 

 ances of wings — " Un examen attentif demontre que ce sont 

 de veritables mains, dont les doigts sont serdement un pen 

 plus allonges." 



The bones of bats are excessively strong, hard, and semi- 

 transparent, the radius is a long bone cnrved laterally and 

 inwards like a bow. Along the convex surface runs the 

 extensor muscle Avith its tendon, which crossing over the 

 carpus becomes connected with the tendons that extend the 

 fingers. On the opposite side of the bone is placed the 

 muscle and tendon that closes the wing. The ulna in bats is 

 either absent or rudimental, the muscles of the forearm are 



