42 11. 9- 



broken. Cartilage and bone are indeed fundamentally the same 

 thing, the differences between them being merely matters of 

 degree.^'' This is manifested in the fact that neither cartilage nor 

 bone, when once cut off, grows again.^^ Now the cartilages of 

 these land animals are without marrow, that is without any dis- 

 tinctly separate marrow. For the marrow, which in bones is 

 distinctly separate, is here mixed up with the whole mass, and 

 gives a soft and mucilaginous consistence to the cartilage. But 

 in the Selachia the chine, though it is cartilaginous, yet contains 

 marrow ; for here it stands in the stead of a bone. 



Very nearly resembling the bones to the touch ^^ are such 

 parts as nails, hoofs, claws, horns, and the beaks of birds, all of 

 which are intended to serve as means of defence. For the 

 organs which are made out of these substances, and which are 

 called by the same names as the substances themselves, the 

 organ hoof for instance and the organ horn, are contrivances to 

 ensure the preservation of the animals to which they severally 

 belong. In this class too must be reckoned the teeth, which 

 in some animals have but a single function, namely the mastica- 

 tion of the food, while in others they have an additional office, 

 namely to serve as instruments of offence ; as is the case with 

 all animals that have sharp interfitting teeth or that have tusks. 

 All these parts are necessarily of a solid and earthy character ; 

 for the value of a weapon depends on such properties. Their 

 earthy character explains how it is that all such parts are much 

 more developed in viviparous quadrupeds than in man. For 

 there is always more earth in the composition of these animals 

 than in that of the human body. However, not only all these 

 parts but such others as are nearly connected with them, skin for 

 instance, bladder, membrane, hairs, feathers, and their analogues, 

 and any other similar parts that there may be, will be considered 

 farther on with the heterogeneous parts. There we shall examine 

 into the causes which produce them, and into the objects of their 

 presence severally in the bodies of animals. For, as with the 

 heterogeneous parts, so with these ; it is from a consideration of 

 their functions that alone we can derive any knowledge of them. 

 The reason for dealing with them at all in this part of the treatise, 

 and classifying them with the homogeneous parts, is that under 

 one and the same name are confounded the entire organs and the 

 substances of which they are composed.^^ But of all these 

 655 b. 



