X INTRODUCTION. 



lu addition to the instances already given, certain fislies, as 

 the Uxocoetus and Dactylopterus, possess the power of su'fetaining 

 true flight. The mechanism that lifts the body of the fish from 

 the water, and upholds it for a short time in the air, is obtained 

 in the pectoral fins, which, in these animals, are enormously de- 

 veloped. The structure of these fins is homologous to that of 

 the anterior extremities of other vertebrates — their form alone 

 being modified to adapt the animal to the medium in which it is 

 placed. Thus we have, in each great subdivision of vertebrate 

 animals, a representative capable of sustaining flight. 



Another somewhat similar modification of the animal economy 

 is met with in a few animals of arboreal habits. Here a peculiar 

 arrangement of the skin is observed, which enables the possessor 

 to break the force of downward leaps. In the Flying Lemur 

 (Galeopithecus), in the Flying Squirrel {Pteromya), and in the 

 Flying Opossum (Petaurista), the furred skin extends laterally 

 from the sides of the body, and is attached to anterior and posterior 

 extremities at the metacarpal and metatarsal regions respectively. 

 The only instance of osteological development is obtained in the 

 Dragon (Draco voJaiis), a small lizard from Sumatra, in which long, 

 transverse processes from either side of the lumbar vertebra? sup- 

 port a thin membranous growth which is capable of being opened 

 and shut by means of muscles atta(.'hed to the bony frame-work. 



Anatomy. — From the consideration of the mechanism of the 

 wings of bats, it is an easy transition to speak of their anatomy. 



The bones of Cheiroidera, though incapable of receiving air 

 from the surrounding medium, are nevertheless of very light 



class it could be assigned. Its peculiarities consist of a continuation of 

 tlie bones of the vertebral colnmn posteriorly to the number of twenty- 

 segments, thus creating a tail seven inches in length ; of the metacarpal 

 bones, being composed of four bones instead of two or tliree as in living 

 birds ; and of the reptilian character of the pelvis. 



For descriptions concerning tliis curious animal the reader is referred to 

 the original paper by M. von Mfyer, toe. cit. ; an article in The Intelltciual 

 Observer, for Dec. 1862 (with plate), by Wm. H. Woodward ; an article in 

 Amer. Journ. Sri. and Arts, 2d series, XXXV, May, 1863, 129 (Prof. Dana); 

 an article in Phil. Trans. CLllI, part I, 1863, 33, pi. 1 to 4 (Prof. Owen). 

 The last mentioned paper is the most complete on the subject, and is 

 accompanied with a handsome full size plate of the fossil. 



It is from this memoir that the outline engraving on the opposite page 

 has in part been taken. ^ 



