EXTERNAL FEATURES 



347 



sisting of three successive parts, the first two slender and the third 

 broad and adapted to be appHed to the ground. The hand has 

 only four digits, that which corresponds to the thumb of man 



B 



Fig. 261. — The right hand of a frog : A, male at breeding season ; 

 B, female ; C, male out of breeding season. 



Pig^- 



sr 



sr 



ier 



d.l^^ 



Fig. 262. — A section of the skin of a frog, taken vertically to the surface, highly 



magnified. 



h.v., Small blood vessels ; cap., capillaries ; d.L, dense layer of connective tissue, consisting of fibres which 

 lie parallel to the surface ; der., dermis or corium ; ep.. epidermis ; gl'-.g!'., gl"'., glands of three kinds ; 

 gl'. and gl". secrete a slimy mucus and pass it to the surface of the skin by ducts which are not shown 

 in the section ; gl'". secretes a more watery secretion which probably contains a substance of unpleasant 

 taste ; all three kinds are simple glands of the saccular type ; h.l.. horny layer of the epidorinis ; 

 M.I., lowest row of the Malpighian layer of the epidermis ; pig., pigment cells ; v./., strands of vertical 

 fibres in the connective tissue. 



