198 SKELETON OF THE BAT, ^ 



is remarkably narrow. The ossa innominata have coa- 

 lesced with the sacruin, but not with each other, the 

 pubic arch remaining open. The bodies of the sacral 

 vertebra? are blended togetlier, and are carinate below; 

 their neural spines have coalesced to form a high ridge. 

 The acetabula look almost directly outwards. The head 

 of the femur has no pit for a round ligament. A fabella 

 is preserved behind the outer condyle. A hamular pro- 

 cess is sent ofi' from the head of the tibia and fibula ; the 

 lower moieties of the shafts of these bones are blended 

 together. The toes are five in number on the hind-feet as 

 in the fore, but are much more feebly developed. Th§y 

 serve to throw back the loose earth detached by the 

 spade-shaped hands. 



SKELETON OF THE BAT. 



The form of limb presented by the arm and hand of 

 the bat, offers the most strikino^ contrast to the burrowino' 



7 O 



trowel of the m.ole. Viewed in the living animal, it is a 

 thin, widely expanded sheet of membrane, sustained like 

 an umbrella by slender raj^s, and flapped by means of 

 these up and down in the air, and with such force and 

 rapidit}^, as, combined with its extensive surface, to react 

 upon the rare element more powerfully than gravitation 

 can attract the weight to which the fore-limbs are attached; 

 consequently, the body is raised aloft, and borne swiftly 

 through the air. The mammal now rivals the bird in its 

 faculty of progressive motion; it flies, and the instru- 

 ments of its aerial course are called "wings." The whole 

 frame of the bat is in harmony with this faculty, but the 

 mammalian type of skeleton is in nowise departed from. 

 The vertebral formula of the common bat {Vespertilio 



