VIL] THE EXTERNAL SKELETON. 237 



supported by the elongated free and movable ribs before 

 noticed, is found in the little Lizards called " Flying Dragons," 

 and a singular fold round the neck exists in the Frilled 

 Lizard. A pouch beneath the throat and long filamentary 

 (merely cutaneous) processes on the back exist in some 

 other Lizards, as in adult male 

 Iguanas. In the Seals a fold of 

 skin connects together the hind 

 legs and the tail ; but the maxi- 

 mum of skin expansion is found 

 in Bats, as we may see in the 



Common BatS Of this Country, F IG. 2 oa.-THE FRILLED LIZARD. 



where not only are the legs and 



tail bound together by a wide fold of skin, but this is continued 

 on to and between the extraordinarily elongated fingers, to 

 form the relatively enormous wings. 



Folds of skin hang freely in some animals, as e.g. the 

 dewlap of cattle ; and peculiar folds are developed in the 

 Rhinoceros, the thickness and denseness of the skin render- 

 ing such folds necessary to allow of free movement of the 

 body and limbs. 



The integument may be much more distensible than in 

 man, as is the case, especially in those Fishes (e.g. Diodon) 

 which blow themselves out with air and then float belly 

 upwards. 



4. The skin of man, as of all other Vertebrates, consists 

 of two LAYERS : an external layer, devoid of nerves and 

 blood-vessels (and consequently of feeling), and a deeper 

 layer, supplied with both, and highly sensitive. The external 

 layer is termed the epidermis? the deeper layer is called the 

 dermis. At the lips the external layer visibly changes in 

 -texture, and inside the lips and mouth it becomes soft and 

 moist, and is termed mucous* membrane. This, however, is 

 a mere modified continuation of the external skin, and it 

 lines the whole of the internal passages which communicate 

 with the exterior. The superficial layer of the skin so 

 reflected inwards is termed epithelium? which is thus but 

 a modified epidermis, and the common term ECTERON 4 is 

 applied to both structures, as the name ENDERON 5 is ap- 

 plied to the] deeper or dermal layer (i.e. the dermis) where- 

 ever situate. 



1 From fTtl and de'pya, skin. 2 From /U?KO, M^fa, an Y slimy substance. 



3 From ewi and #u\Xu>, to grow. 4 From t, out of, and <5fpo, skin. 

 5 From ei-, within, and <3e'po. 



