22 _ GENERAL CHARACTERS OF MAMMALIA. 



interior of which seems to be filled with a pulpy matter. With 

 most animals they are cylindrical and larger at the base than at 

 the summit ; they are often more or less flattened ; there are 

 some which are lamellar and similar to a slip of grass ; some- 

 times their surface seems to be perfectly smooth, at others 

 channelled, or armed with slight asperities, or even presenting a 

 necklace-like (moniliform) aspect ; finally, their size, form and 

 elasticity vary very much in different animals and in the different 

 hairs of the same individual. 



8. The names by which the different varieties of hairs are 

 distinguished, differ according to the nature of these horny fila- 

 ments, and according to the parts whereon they grow. They 

 are called quill* or spinet, when they are very thick, pointed, and 

 stiff, and when they resemble thorns, (as in the porcupine) ; 

 bristles, when not so thick and less resisting, but still, very stiff, 

 except towards their extremities; hairs do not differ much from 

 bristles except in being somewhat longer and not so thick; like 

 bristles, they are generally straight, though they are sometimes 

 curly, particularly when very long. Wool is a species of long 

 hair, very fine, and contorted in every direction : and down or 

 fur is composed of hairs of extreme fineness and softness, and 

 is generally found beneath a layer or covering of stouter hairs. 



9. All the mammalia, except the cetacea, (that is, dolphins, 

 porpoises, &c.) have two pairs of extremities or members, 

 namely ; one pair of thoracic or anterior, or upper extremi 

 ties, and one pair of posterior (inferior) or abdominal extremi 

 ties; but in the cetacea this jatter pair is absent, and conse- 

 quently, there only exists the thoracic members The structure 

 of all these animals is nearly the same as that of man, and the 

 differences observed, principally depend upon the relative length 

 of the different bones, and the number of fingers, which never ex- 

 ceeds five. 



10. The conformation of the extremities varies somewhat ac- 

 cording to the uses for which they are designed. They may serve 

 1. For walking, leaping, &c.; 2. For prehension and touch; 

 3. For burrowing in the earth ; 4. For swimming ; and 5. For 

 flying; and when they are best adapted to the performance of 

 one of these functions, they are in a very slight degree, or not 

 at all suited to the others. 



8. When do hairs take the name of quills or spines ? What are bristles ? 

 What is wool ? What is fur ? What is down ? 



9. How many extremities have the mammalia ? 



U). is the conformation of the extremities the same in all the mammalia ? 



