G12 ANATOMY OF VERTEBRATES. 



one: by this modification of the dermal plates the little animal 

 is enabled to roll itself into a ball, and protect its snout and 

 legs beneath the trunk-armour. In the large extinct Armadillos 

 (Glyptodon) the annular or banded modification of the armour 

 was not present; and the whole of the dermal scutes of the trunk 

 were united into one massive domed roof: the marginal scutes 



o 



being generally triangular, the rest more or less regularly hexa- 

 gonal. The inner surface of the scutes, imbedded in the derm, 

 is smooth ; the outer surface coated with epiderm is sculptured 

 in a definite pattern, distinct for each species and characteristic 

 thereof. The dermal plates of the caudal sheath in certain kinds 

 of Glyptodon formed annular series of large conical tubercles : 

 the first ring, in all, Avas distinct from the rest of the caudal 

 sheath, to facilitate the movements of the tail. 



In the Pangolins (J\Ja.ni^ the exterior of the derm is grooved, 

 as in Lizards, for the lodgment of the bases of the large horny 

 scales, which protect the body and tail by their imbricated over- 

 lapping arrangement (vol. ii. fig. 158). The muscular tissue 

 enters in greater proportion than usual into the composition of the 

 derm of this Mammal, in connection with the thick ' panniculus 

 carnosus,' and in relation to the erection of the scales, when the in- 

 tegument is drawn defensively about the uprolled trunk and tail. 



Productions or duplications of the derm, with included muscles, 

 &c., form the peculiar mammalian oral appendages called 'lips: ' 

 an everted fold of skin forms the ' scrotum : ' an inverted fold 

 the marsnpium and the cheek-pouch (p. 386, fig. 300) : the 

 derm is extended between the digits to form the ' web ' in most 

 aquatic quadrupeds, and also beyond the digits to augment the 

 swimming surface in the Ornithorhynchus : a duplicature of 

 integument forms the ' dewlap ' in certain Bovines : it forms a 

 broad fold on each side, continued from the fore to the hind 

 limbs to form the parachute, in the Petaurists, Pteromyds 

 (Vol. ii. fig. 156), and Flying Dormice (Anomalurus): in the 

 Colugos (G(ih'opitheeus) the dermal ibid expands from the nape 

 to the fore-feet, from these to the hind-feet, and thence to the tip 

 of the tail, forming a triangular ' interfemoral ' flap. But the 

 most extraordinary developments of derm arc presented by the 

 Bat tribe (vol. ii. p. 278, fig. 156) : the ' antibrachial fold ' crosses 

 the deep interspace between the humerus and radius ; the ' digital 

 fold,' which mainly forms the wing, occupies the interspaces of 

 the long and attenuated digits ; the ' flank-folds ' extend from the 

 fifth digit to the tarsus ; the ' interfemoral fold ' passes from leg- 

 to leg, intercepting more or less of the tail. 



