20 



NATURAL HISTORY OF VERTEBRATE ANIMALS 



death-feigning and to the hypnotic state in man, is a matter of 

 doubt. 



The use of the hmbs in other vertebrate animals shows many- 

 interesting features. Relationships between structure and func- 

 tion are everywhere apparent. Typically, the skeleton of each 

 limb consists, as in the human body, of an upper portion supported 

 by a single bone, the femur in the leg and the humerus in the arm ; 

 a portion containing two bones, the tibia and fibula of the leg, and 

 the radius and ulna of the arm; a group of smaller bones at the 

 ankle or wrist ; and the bones of foot or hand. This plan of struc- 

 ture, which appears in the generalized condition in man and some 



Fig. 10. — Death feigning in young toads that have been seized and held for a 

 moment, sometimes called hypnotism but probably not comparable with the 



hypnotic state in man. 



(From Dickerson, "Frog Book," copyright, 1920, by Doubleday Page & Co., reprinted 

 by permission.) 



of the less specialized of the terrestrial vertebrates (Fig. 18, p. 39), 

 is modified in a variety of ways for different uses, but persists 

 throughout as a type to which the most specialized forms can be 

 referred. Parts suppressed in the adult are often found in the 

 embryo. Hence, it is in general supposed that limbs Hke those of 

 the horse or the bird, with their smaller number of bones, have 

 reached their present state by loss or fusion of parts in the course 

 of evolution {cf. Fig. 277, p. 517). Often these fusions are readily 

 seen, as in the radio-ulna or tibio-fibula of the frog (Fig. 40, p. 69). 

 Miscellaneous Activities. — Sound production by frogs and 

 toads is more diversified than is commonly supposed. One who has 

 trained himself in this regard can distinguish the notes of different 

 species as he can those of birds, although there is much less range 



