MAMMALIA. 



555 



Fig. 381. — Lateral 

 View of the Ster- 

 num OF A Fox-Bat 



{Pteroptis). 



but in the mole the forelimb is shortened, not length- 

 ened, as the medium upon which the work is done is 

 solid earth, not air. 



The pelvis of the bat is produced backwards and there 

 is usually no pelvic symphysis. The hind-limbs are small. 

 The fibula is a small splint-like bone down the side of the 

 tibia. There are five toes, of which the first is slightly 

 the smallest : they bear curved claws. 

 As in the mole and porpoise, the adap- 

 tation has resulted in increase of the 

 fore-limb and reduction of the hind- 

 limb. 



The stomach of the fox-bat is simple, 

 though the pyloric portion is produced 

 into a process. 



The mammae of the bat are pec- 

 toral and paired. The fecundity is low, 

 as is natural when the parent has to 

 carry the family about with her, cling- 

 ing to her under- surface. Such a 

 position of the young may account for 

 the pectoral mammae. 



The adaptation of the bat to an 

 aerial habit may be summarised as 

 follows : — (i) Fore-limbs and four digits 

 elongated, supporting " wing mem- 

 brane." (2) Hind-limbs bent back- 

 wards and assisting to support ^'wing 

 membrane" and " interfemoral mem- 

 brane." (3) Keeled sternum, connected 

 by large clavicle to scapula. (4) Partial 

 ankylosis of dorso-lumbar vertebrae. (5) 

 Great development of hearing and of 

 '^ motion sense." (6) Small fecundity and pectoral mammae. 



Note discontinuous keel. 



^rial Adaptation. 



Tlie ^rial types are modified from the arboreal, a* short step only 

 intervening between the two. As examples we may instance the flying 

 "squirrels" and phalangers of Australia {Cusais, Petatcrtts), the true 



* Probably connected with arboreal habit which preceded that of flight (c/. 

 Primates). 



