3438. The tongue is indeed mostly fleshy and soft; yet in many species it is provided with horny points, in others invested by a dense coriaceous tegument, so that it appears to represent an instrument for deglutition rather than gustation.
3439. The lips also are mostly fleshy and moveable; yet in many they retrograde exceedingly and lose their mobility, as is partly the case in the Ornithorynchus.
3440. In most, however, the limbs, especially the toes, are still subject to variation. Their perfection consists in the number five, and in the difference between the two pairs of limbs, as in Man. In the Apes the posterior feet are also hands, which is an imperfection; in the Marsupials there are hands posteriorly but toes in front; in other respects there are generally toes, sometimes five, then four, finally two perfect and two dew-claws in the Ox, and at length only one in the Horse, while the posterior extremities are virtually lost in the Whales.
3441. The dental system, as being the set of maxillary claws, is alone present in its state of perfection in the Thricozoa. They alone have, in addition to the incisor teeth, all the five kinds of teeth that differ from each other in form, namely, canine, false molars, laniary, with second and third true molars, corresponding to the five fingers reckoned from the thumb.
3442. In the dentition of those animals which tear their food the greatest amount of completeness and variety is met with, since each tooth has a different form and function.
In the Bears the molars are uniform in character, and so on through the Apes up to Man.
In the Marsupials they are tolerably similar, as also in the Bats and Shrew-mice.
They are still more alike in the Pig and Horse, and the incisor teeth begin to be wanting in the Ruminantia, e. g. the Ox.
In Mice the canines are wanting, in the Sloths the front teeth, and in the Ant-eaters actually all.
3443. In opposition to the perfect eye the general sense of feeling is developed in the tegument. The tegument which is best developed will be that, which represents a self-substantial organ with all its appurtenances, and thus an organ of touch, whose nobility of rank consists in motion. A skin, which is moveable by means of muscles, must take the noblest rank. A skin with tegumental muscles is an organ of feeling, which is already in some degree subjected to the influence of the will. If tegumental muscles do not occur in all these animals, they still do in most of them.