OF THE ATTITUDES AND OF LOCOMOTION. 



153 



Some squirrels, and the Galeopitheci, have a wide ex- 

 pansion of the common integuments extending on either 

 side, from the neck to the tail 

 and hinder extremities; and by 

 this they can support themselves 

 in the air for a short time; it 

 answers, in fact, the purpose of 

 a parachute. 



In the vertebrata, the wings 

 are always formed by the pectoral 

 extremities, without requiring on 

 the part of the limb any very ex- 

 traordinary metamorphosis. The 

 figure (108) representing the 

 skeleton of the bat explains this 

 sufficiently; the phalanges of the 

 fingers are much extended, and 

 with them the integuments. 



The wings of birds, which at 

 first sight seem to differ essentially 

 from the arm of man, the foot of 

 the horse, and the swimming 

 paw of the whale, in point of 

 fact do not differ as regards 

 the basis of the instrument, the skeleton. To the bones 

 representing the fore-arm and hand, analogous to those 

 of man, are attached the powerful feathers of the wing; the 

 hand is small, and the digital portion merely rudimentary ; 

 but the basilar portion of the limb is always powerful, and 

 perfectly adapted for flight. 



The wings of insects are constructed pretty nearly on the 

 same plan as those of birds, but the tegumentary part is 

 supported on horny stalks, instead of osseous, as in the 

 vertebrata. 



295. Organs of Prehension. By slight modifications 

 in the form of the bones, and in the disposition of the articu- 

 lations, the limbs become instruments of prehension, instead 

 of mere locomotion and support. To be satisfied of this, it is 

 only necessary to compare the pectoral and abdominal 

 extremities in man, section by section, and bone by bone ; 

 the rotation of the radius, and the con sequent movements of 

 pronation and supination, together with an opposing thumb, 

 constitute in reality the chief differences between the arms 



Fig. 107. Galeopithecus. 

 Flying Lemur. 



The 



