n INTRODUCTION. 



of the genera discussed. In the Systematic Index the arrange- 

 ment of the Families, Genera, and Species according to this method 

 of classification may be seen ; and notes on the natural position of 

 each genus and species will be found in most cases attached to the 

 definitions and descriptions throughout the work. 



Instead, therefore, of reopening this subject, I think it preferable to 

 occupy the space remaining at my disposal with an account of the Com- 

 parative Anatomy and Geographical Distribution of the species. 

 In treating of the Comparative Anatomy I shall limit my remarks 

 especially to those parts of the body which present the greatest 

 variability in form, as a knowledge of the chief structural modifica- 

 tions, both external and internal, is all-important in systematically 

 arranging the species. 



Of all the orders of Mammalia none are so well defined as the 

 Chiroptera : the presence of true wings at once distinguishes them ; 

 and this peculiarity is accompanied by other modifications of bodily 

 structure having relation to aerial locomotion. Thus, in direct con- 

 trast to aU other mammals (in which locomotion is chiefly effected 

 by action from behind, and the hind limbs greatly preponderate in 

 size over the fore), in the Chiroptera the fore limbs, being the only 

 agents in propelling the body forward during flight, immensely 

 exceed the short and weak hinder extremities ; the thorax giving 

 origin to the great muscles which sustain flight, and containing the 

 proportionately very large lungs and heart, is remarkably capacious, 

 and the ribs are flattened and close together ; the shoulder-girdle 

 also is greatly developed in comparison with the weak pelvic bones. 

 Other structural modifications secondary to these are observable in 

 the form of the bony skeleton, in the integumentary system, in the 

 alimentary canal, and in other parts of the body, which I now pro- 

 ceed to describe under their several heads. 



Osseous System:. 



The bones entering into the formation of the skeleton in Chiro- 

 ptera are characterised by their slenderness, and by the great size of 

 the medullary canals in those forming the extremities. The verte- 

 bral column is short, and the vertebrae differ very slightly in number 

 and form throughout the species. The general number of the 

 thoracico-lumbar vertebrae is 17, whereof 12 are thoracic and 5 

 lumbar. Occasionally species of the same family differ more from 

 each other in the number of vertebrte than species of very distinct 



