90. THE EXTERNAL EAR.--The external portion of the organ of hearing, designated in Fig. 53, A, includes, first, that outer part (_a_), which is commonly spoken of as "the ear," but which in fact is only the portal of that organ; and, secondly, the _auditory canal_ (_b_). The former consists of a flat flexible piece of cartilage, projecting slightly from the side of the head, attached to it by ligaments, and supplied with a few weak muscles. Its surface is uneven, and curiously curved, and from its resemblance to a shell, it has been called the _concha_. It probably serves to collect sounds, and to give them an inward direction; although its removal is said not to impair the acuteness of hearing more than a few days. {218} [Sidenote: 91. The ear in the animals of delicate hearing? Rabbit? Fishes?] 91. In those animals whose hearing is more delicate than that of man, the corresponding organ is of greater importance, it being larger and supplied with muscles of greater power, so that it serves as a natural kind of ear-trumpet, which is easily movable in the direction of any sound that attracts the attention of the animal. Bold, predaceous animals generally have the concavity of this organ directed forward, while in timorous animals, like the rabbit, it is directed backward. Fishes have no outer ear, but sounds are transmitted directly through the solid bones of the head, to the internal organ of hearing. [Illustration: FIG. 53.--THE EAR AND ITS DIFFERENT PARTS. A, Diagram of the Ear. _a_, _b_, External Ear. _c_, Membrane tympani. _d_, Middle Ear. _e_, Internal Ear. B to B''', Bones of the Middle Ear (magnified). C, The Labyrinths, or Internal Ear (highly magnified).] [Sidenote: 92. What is the auditory canal? Describe it.] 92. The _auditory canal_ (Fig. 53, A, _b_), which is continuous with the outer opening of the ear, is a blind passage, an inch and a quarter in length, its inner extremity being bounded by a closely-fitting, circular membrane. This canal is of oval form, is directed forward and inward, {219} and is slightly curved; so that the inner end is ordinarily concealed from view. The pouch of the skin which lines this passage is smooth and thin, especially at the lower end, where it covers the membrane just mentioned. [Sidenote: 93. How is it guarded and protected? Ear-wax?]