APPENDICES OF THE SKIN. 99 
although very remarkable exertions are Eeeqeaaaly made by 
the system to repair the loss *. 
4. Scales.—'These vary remarkably in thei form, struc- 
ture, mode of adhesion, and situation in different animals. 
In general they are flat plates, variously marked. In some 
cases, each scale consists of several plates, the lowest of 
which are largest ; so that the upper surface becomes some- 
what imbricated. Some scales adhere by the whole of their 
central surface; while others resemble the human nail, in 
having the distal extremity free. 
The composition of scales is similar to that of the cuticle, 
with the addition of some earthy salts. They appear to be 
inserted in that layer of the skin, and to resemble it in many 
of their properties. When rubbed off, they are easily re- 
newed, and frequently experience the same periodical reno- 
vations as the cuticle. In some cases, the cuticle may be 
observed extended over them, as in the armadillos. In ge- 
neral, however, it only surrounds their base. They derive 
their colour from the mucous web on which they are placed. 
In quadrupeds, scales occur, covering the whole body 
like a coat of mail, in the armadillos ; or certain parts only, 
as the tail of the beaver and rat. In birds, the scales are 
found only on the feet. In reptiles, they occur of every 
part of the body, and are placed Jaterally in some ; while, 
in others, they are imbricated like the slates of a house. In 
fishes, the scales are usually imbricated, with the distal edge 
free, and the epidermis envelopmeg their base. In some m- 

* Tuxtpius notices some curious cases of this kind, which fell under his 
own observation :—‘* Ungues in digitorum apicibus, semel deperditos, ite- 
rum renasci novum non est, sed raro id conspicitur fieri, in sccundo aut ter- 
tio articulo, prioribus amputatis, in quibus tamen non scmel eosdem vidimus 
non secus progerminare debitamque acquirere formam, ac si in digitorum 
consisterent apicibus, deponente nunquam solicitudinem suam officiosa na- 
tura.”——Observationes Medica, lib. iv. cap. 56. 
0) 
Ge 
