On The Parts Of Animals   

neighbouring viscera. The exception of which mention was made is the
belly. The walls of this are in all animals devoid of bones; in order
that there may be no hindrance to the expansion which necessarily
occurs in this part after a meal, nor, in females, any interference
with the growth of the foetus, which is lodged here.
Now the bones of viviparous animals, of such, that is, as are not
merely externally but also internally viviparous, vary but very little
from each other in point of strength, which in all of them is
considerable. For the Vivipara in their bodily proportions are far
above other animals, and many of them occasionally grow to an enormous
size, as is the case in Libya and in hot and dry countries generally.
But the greater the bulk of an animal, the stronger, the bigger, and
the harder, are the supports which it requires; and comparing the big
animals with each other, this requirement will be most marked in those
that live a life of rapine. Thus it is that the bones of males are
harder than those of females; and the bones of flesh-eaters, that get
their food by fighting, are harder than those of Herbivora. Of this
the Lion is an example; for so hard are its bones, that, when struck,
they give off sparks, as though they were stones. It may be mentioned
also that the Dolphin, in as much as it is viviparous, is provided
with bones and not with fish-spines.
In those sanguineous animals, on the other hand, that are oviparous,
the bones present successive slight variations of character. Thus in
Birds there are bones, but these are not so strong as the bones of the
Vivipara. Then come the Oviparous fishes, where there is no bone, but
merely fish-spine. In the Serpents too the bones have the character of
fish-spine, excepting in the very large species, where the solid
foundation of the body requires to be stronger, in order that the
animal itself may be strong, the same reason prevailing as in the case
of the Vivipara. Lastly, in the Selachia, as they are called, the
fish-spines are replaced by cartilage. For it is necessary that the
movements of these animals shall be of an undulating character; and
this again requires the framework that supports the body to be made of
a pliable and not of a brittle substance. Moreover, in these Selachia
nature has used all the earthy matter on the skin; and she is unable
to allot to many different parts one and the same superfluity of
material. Even in viviparous animals many of the bones are
cartilaginous. This happens in those parts where it is to the
advantage of the surrounding flesh that its solid base shall be soft
and mucilaginous. Such, for instance, is the case with the ears and
nostrils; for in projecting parts, such as these, brittle substances
would soon get broken. Cartilage and bone are indeed fundamentally the
same thing, the differences between them being merely matters of
degree. Thus neither cartilage nor bone, when once cut off, grows
again. Now the cartilages of these land animals are without marrow,
that is without any distinctly 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, whether solid or cloven, 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 mastication of the food, while in others they have an
additional office, namely to serve as weapons; as is the case with all
animals that have sharp interfitting teeth or that have tusks. All
these parts are necessarily of 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 more developed in