The Rhinoceros, the Tapir, and the Hippo potamus have likewise only tvvo mammm, but they are placed beneath the belly.
ln the Hog there are generally ten nipples both in the male and female; these are situated beneath the belly, five on each side, but some times there are five on one side and six on the other, and occasionally six on both sides.
Of the Nervous .System. Brain.—The brain in the Pachydermata is largely developed, and the convolutions upon its surface comparatively small,though very numerous and separated from each other by deep sulci. In the Elephant the absolute size of the organ exceeds that of man, but is very small in proportion to the bulk of the animal, especially when we take into the ac count the great size and intellectual aspect of the head. In an Elephant dissected by the Parisian Academiciaus, which was seven feet and a half high from the ground to the top of the back, and eight feet and a half in length from the forehead to the tail, the brain and cerebellum together weighed nine pounds. The convolutions upon the surface of the cerebrum were well marked, and the proportionate size of the cerebelluin is described to have been enormous; the brains of the Rhinoceros and Tapir are equally large in proportion, but the relative size of the cerebrum, especially of its anterior and superior regions, when compared with the rest of the brain, is much less. The h ippocampus and corpus stria tum are well developed, and the lateral ventri cles are continued forwards into the dilated olfactory bulbs. The cerebellum is very large and expanded transversely, its surface being still further increa.sed by numerous and complex anfractuosities. The pons Varolii corresponds in size with the developement of the lateral lobes of the cerebellum, anti the corpora oli varia are remarkably prominent. In other re spects the brain of the animals included in this order presents no peculiarities worthy of special notice. The nerves take their rise in the usual manner, and have the same distribution as in other Mammalia. In those races, however, which have the nose largely developed, the fifth pair is reraarkable for its great size, and in the Proboscidian species these nerves are of enormous dimensions.
The dura mater is very thick, proportioned rather to the size of the skull and of the entire animal than to that of the brain itself; and its two fibrous layers are found in the larger species t,o be separated by a quantity of cellular substance in which the vessels ramify.
The spinal chord presents no peculiarity worthy of being distinctly alluded to.
Of the Special Senses. Touch.—In animals whose limbs seem to be converted into mere pillars of support, and whose hoof-eased feet are totally destitute of all power of prehension, it would hardly have been expected that any nicety of appreciating tactile impressions should exist in the situations usually appropriated to this sense, more especially when we take into the account the thickness and density of the integu ment with which they are clothed.
The nasal apparatus, however, in all the Pachydermata, is ,richly endowed with nerves of sensation, and obviously forms a very per fect organ of touch. It is moreover in some measure converted into -an instrument of pre hension, or is employed for digging the soil in search of food, as well as for the usual offices assigned to it; in fact it is in this group of quadrupeds alone that the nasal cartilages and the muscles of the nose assume their full deve lopernent, and accordingly will merit special notice in this place.
In the Hog the cartilages of the nose form a complete tube, which is a continuation of the bony nostrils, and near the end of the snout, in the vicinity of the septum nariewr, the extremity of the cartilages becomes ossified, and in the dried skull seems to form an addi tional bone Org. 481). Four strong pairs of muscles, derived from the bones of the face, confer upon the organ considerable power of motion, and render it very efficient in tearing up the earth. Of these muscles the first pair arises in front of the orbit from the lacrymal bone, and terminates in a strong tendou which spreads out upon the upper aspect of the nmal atrtilages. 'Iwo other pairs situated benenli the preceding are derived from the superior maxillary bone in front of the zygomatic pro cess : these muscles are pargally united, but their tendons run separately to be inserted, one into the side, the other into the base of the snout. The fourth pair is comparatively of small size, arising from the nasal bone, and running obliquely beneath the tendons of the two last, terminates near their insertion. The snout and all the above longitudinal muscles are moreover enclosed by a layer of annular fibres, which are a continuation of the orbicularis oris, so that considerable mobility in any required direction is thus amply provided for.