The following statement, therefore, by Sir S. Baker is inexplicable, namely, that a rhinoceros, which he shot in North Africa, "had no ears; they had been bitten off close to the head by another of the same species while fighting; and this mutilation is by no means uncommon."
Lastly, with respect to monkeys. Some kinds, which have moveable ears, and which fight with their teeth--for instance the _Cereopithecus ruber_-- draw back their ears when irritated just like dogs; and they then have a very spiteful appearance. Other kinds, as the _Inuus ecaudatus_, apparently do not thus act. Again, other kinds--and this is a great anomaly in comparison with most other animals--retract their ears, show their teeth, and jabber, when they are pleased by being caressed. I observed this in two or three species of Macacus, and in the _Cynopithecus niger_. This expression, owing to our familiarity with dogs, would never be recognized as one of joy or pleasure by those unacquainted with monkeys.
 `The Nile Tributaries of Abyssinia,' 1867, p. 443.
_Erection of the Ears_.--This movement requires hardly any notice. All animals which have the power of freely moving their ears, when they are startled, or when they closely observe any object, direct their ears to the point towards which they are looking, in order to hear any sound from this quarter. At the same time they generally raise their heads, as all their organs of sense are there situated, and some of the smaller animals rise on their hind-legs. Even those kinds which squat on the ground or instantly flee away to avoid danger, generally act momentarily in this manner, in order to ascertain the source and nature of the danger. The head being raised, with erected ears and eyes directed forwards, gives an unmistakable expression of close attention to any animal. CHAPTER V.
SPECIAL EXPRESSIONS OF ANIMALS.
The Dog, various expressive movements of--Cats--Horses--Ruminants--Monkeys, their expression of joy and affection--Of pain--Anger--Astonishment and Terror.
_The Dog_.--I have already described (figs. 5 and 1) the appearance of a dog approaching another dog with hostile intentions, namely, with erected ears, eyes intently directed forwards, hair on the neck and back bristling, gait remarkably stiff, with the tail upright and rigid. So familiar is this appearance to us, that an angry man is sometimes said "to have his back up." Of the above points, the stiff gait and upright tail alone require further discussion. Sir C. Bell remarks that, when a tiger or wolf is struck by its keeper and is suddenly roused to ferocity, every muscle is in tension, and the limbs are in an attitude of strained exertion, prepared to spring. This tension of the muscles and consequent stiff gait may be accounted for on the principle of associated habit, for anger has continually led to fierce struggles, and consequently to all the muscles of the body having been violently exerted. There is also reason to suspect that the muscular system requires some short preparation, or some degree of innervation, before being brought into strong action. My own sensations lead me to this inference; but I cannot discover that it is a conclusion admitted by physiologists. Sir J. Paget, however, informs me that when muscles are suddenly contracted with the greatest force, without any preparation, they are liable to be ruptured, as when a man slips unexpectedly; but that this rarely occurs when an action, however violent, is deliberately performed.
 `The Anatomy of Expression,' 1844, p. 190.
With respect to the upright position of the tail, it seems to depend (but whether this is really the case I know not) on the elevator muscles being more powerful than the depressors, so that when all the muscles of the hinder part of the body are in a state of tension, the tail is raised. A dog in cheerful spirits, and trotting before his master with high, elastic steps, generally carries his tail aloft, though it is not held nearly so stiffly as when he is angered.