On the Sense of Feeling. 303 



plumage by the latter, in the relative thickness of the cutis, in the almost 

 total absence of pigment, in the substitution of a bill for the dental sys- 

 tem, and in the prodigious development of the phaneric system by which 

 the feathers are secreted. 



The integument of birds is composed of the same parts with that of man. 

 The cutis is usually tiiin, especially over those parts covered by plumage ; 

 on the legs and feet, however, it is very thick. It is also thick in aquatic 

 birds, and those iniiabiting cold climates, being moreover replenished by a 

 subcutaneous layer of fat. 



The vascular portion is more highly developed than in any other class 

 of animals, the organs which secrete the feathers requiring a copious sup- 

 ply of blood. 



The pigment, wanting over the body, appears upon the legs and feet. 

 The nervous layer is not particularly evident. 



Where the plumage is thick, the epidermis is scarcely perceptible j but 

 where there are no feathers, as upon the legs and feet, and more especially 

 upon the under surface or soles of the latter, is it well developed. The 

 callosity upon the breast of the ostrich and cassowary, against which those 

 birds rest when sleeping, is ej)idermoid. 



The cryptic system in birds is chiefly developed about the back and 

 neighbourhood of the tail; and its secretion is in many aquatic birds very 

 profuse, and of a rancid odour. 



The phaneric system, though modified to secrete feathers, resembles, in 

 its general arrangement, that which has been already described as se- 

 creting hair. 



Besides the claws with which the feet of birds are provided, a few, as 

 the ostrich, have something analogous to them upon their upper extremity ; 

 that bird has two on each wing. 



The beaks of birds are occasionally, as in the duck, organs both of taste 

 and touch ; but the general sense of tact is not very strikingly exhibited 

 in this class, and their feet, with the exception above mentioned, form al- 

 most the sole organ of touch. 



If we examine the bird's foot, we shall find the cushion which forms the 

 sole to be perhaps the softest part of the body. This is true even of ostriches 

 and ambulatory birds, and, in a very remarkable degree, of birds of prey. 



We have observed, that as we ascended in the scale, the different parts 

 composing the integument became more distinctly visible j and this we 

 shall find to be very obviously the case with the mammalia. 



In tiic mammalia, the dermis, though very variable in thickness, is al- 

 ways more or less moveable on the parts beneath, the subjacent tissue 

 being never, as in the heads of the turtles and legs of the birds, wholly 

 wanting. There are, however, parts at which the integument is more 

 adherent than elsewhere, as along the median line, on the tail, &c. 



In the mammalia, generally, the integument is thicker upon the back 



