^8 SCIENCE OF AGRICULTURE. Part II. 



Chap. II. 

 Animal Anatomy. 



1806. The leading organs of animal striLCture f may be conveniently arranged as ex- 

 ternal and internal. 



Sect. I. External Anatomy of Animals. 



1807. All animals agree in possessing an exterior covering, or skin, to modify their sur- 

 face, regulate their form, and protect them from the action of surrounding elements. In 

 the more perfect animals, this organ consists of the following parts : the cuticle, the 

 ^jorpus mucosum, the corium, the panniculus, and the cellular web. 



1808. The cuticle is destitute of blood vessels, nerves, and fibres, and usually consists of a thin transparent 

 membrane possessing little tenacity. In those animals which live on the land, it is more rigid in its tex- 

 ture, and scaly and dry on its surface, than in those which reside in the water. In aquatic animals, it is in 

 general smooth, often pliable ; and, in many cases its texture is so soft and delicate, that it appears like 

 mucus. It assumes, likewise, other appearances, such as scales, nails, shells and plates, which deserve the 

 attentive consideration of the naturalist, as furnishing him with important characters for the arrangement 

 of animals. 



1809. The mucus web occurs immediately underneath the cuticle, from which, in general, it may be 

 easily disjoined ; but it is often so closely attached to the true skin below, as not to be separated even by 

 maceration in water. 



1810. The corium (Cutis vera), or true skin, lies immediately underneath the cuticle or mucus web. It 

 is usually destitute of color. It consists in some animals, as quadrupeds, of solid fibres, which cross one 

 another in every possible direction, and form a substance capable of considerable extensibility and elasti- 

 city. It is more obviously organized than the two members by which it is covered. Blood vessels and 

 nerves penetrate its substance, and may be observed forming a very delicate net work on its surface. 



1811. The muscular web varies greatly in its appearance according to the motions which the skin and its 

 appendices are destined to perform. It consists of a layer of muscles, the extremities of whose fibres are 

 inserted into the corium externally, and adhere to the body internally in various directions. This layer is 

 very obvious in the hedgehog and the porcupine, to assist in rolling up the body and moving the spines, 

 and in birds, in the erection of their feathers. In man it can scarcely be said to exist, unless in the upper 

 parts, where cutaneous muscles may be observed, destined for moving the skin of the face, cheeks, and head. 

 Jn the skin of the frog, the only cutaneous muscles which can be observed, are seated under the throat ; the 

 skin on the other parts of the body being loose and unconnected with the parts beneath. The use of this 

 layer of the integument, is to corrugate the skin, and elevate the hairs, feathers or spines with which 

 it is furnished. 



1812. The cellular web forms the innermost layer of the common integuments, and 

 rests immediately on the flesh of the body. It consists of plates crossing one another 

 in difierent directions, and forming a cellular membrane, varying in its thickness, tena- 

 city, and contents, according to the species. In frogs it does not exist. The cells of 

 this membrane are filled with various substances, according to the nature of the animal. 

 In general they contain fat, as in quadrupeds and birds. In some of these the layer is 

 interrupted, as in the ruminating animals, while it is continuous in others, as the boar and 

 the whale. In birds, while a part of this web is destined for the reception of fat, other 

 portions are receptacles for air. In the moon-fish the contained matter resembles albu- 

 men in its chemical characters. 



1813. The appendices of the skin are hairs, feathers, horns, scales, shells, and crusts. 



1814. Hairs differ remarkably not only in their structure, but likewise in their situation. In some cases 

 they appear to be merely filamentous prolongations of the cuticle, and subject to all its changes. This is 

 obviously the case with the hair which covers the bodies of many caterpillars, and which separates along 

 with the cuticle, when the animal is said to cast its skin. In true hair the root is in the form of a bulb, 

 taking its rise in the cellular web. Each bulb consists of two parts, an external, which is vascular, and 

 from which the hair probably derives its nourishment ; and an internal, which is membranous, and forms 

 a tube or sheath to the hair during its passage through the other layers of the skin. From this bulb, and 

 enveloped by this membrane, the hair passes through the corium, mucus web, and cuticle. It usually 

 raises up small scales of this last layer, which soon become dry and fall off, but do not form the external 

 covering of the hair as some have supposed. The hair itself consists of an external horny covering, and 

 a central vascular part, termed medulla oi pith. This horny covering consists of numerous filaments placed 

 laterally, to which different kinds of hair owe their striated appearance. These filaments appear of unequal 

 lengths, those nearest the centre being longest ; and, consequently, the hair assumes the form of an 

 <;longated cone, with its base seated in the skin. This form gives to the hair that peculiar property on 

 which the operation of felting depends. In consequence of this structure of the surface, if a hair is seized 

 at the middle between two fingers, and rubbed by them, the root will gradually recede, while the point of 

 the hair will approach the fingers ; in other words, the hair will exhibit a progressive motion in the direc- 

 tion of the root, the imbricated surface preventing all motion in the opposite direction. It is owing to 

 this state of the surface of hairs, that woollen cloth, however soft and pliable, excites a disagreeable sen- 

 sation of the skin in those not accustomed to wear it. It likewise irritates sores by these asperities, and 

 excites inflammation. The surface of linen cloth, on the other hand, feels smooth, because the fibres of 

 which it consists possess none of those inequalities of surface by which hairs are characterised. 

 - 1815. If a quantity of wool be spread upon a table, covered with a woollen cloth, and pressed down in 

 different directions, it is obvious that each hair will begin to move in the direction of its root, as if it had 

 been rubbed between the fingers. The different hairs thus moving in every direction become inter- 

 woven with each other, and unite in a continuous mass. This is the felt with which hats are made. Curled 

 hairs entwine themselves with one another more closely than those which are straight, though flexible, as 

 they do not, like these, recede from the point of pressure in a straight line; and hence hatters employ 

 various methods to produce curl in the short fur of rabbits, hares, and moles, which they employ. This 

 is accomplished chiefly by applying the solution of certain metallic salts to the fur by a brush; so that, 

 when the hairs are dry, the surface which was moistened, contracts more than the other, and produces 

 the requisite curve. 



1816. It is owing to the asperities of the surf ace~of hair that the spinning of wool is so difficult. This is 

 in a great measure removed, by besmearing it with oil, by which the inequalities are filled up, or, at least. 



