The mouth is lined throughout with a white membrane, which becomes continuous at the lips, and borders with the common integument, where it becomes of a dark brown or black color. The eyes are small, and are furnished with eyelids. They are situated above and behind the angle of the mouth, at the widest part of the head. At a short distance behind the eyes are the external openings of the ears, of sufficient size to admit a small quill, and unprovided with any external auricular appendage. The fins are not far from the posterior angle of the mouth, and are analogous in their formation to the anterior extremities of other animals. They are not much used as instruments of progression, but probably in giving a direction to motions in balancing the body, in sinking suddenly, and occasionally in protecting and supporting their young. [Illustration: SPERM WHALE.] In a full-grown male sperm whale of the largest size the dimensions may be given as follows: Length, from eighty to ninety feet; depth of head, from ten to twelve feet; breadth, from seven to ten feet; depth of body, from sixteen to eighteen feet; swimming paws, or fins, about eight feet long and three broad; the tail, or flukes, have been previously mentioned. In reviewing the description of the external form and some of the organs of the sperm whale, it will, perhaps, not be uninteresting if some comparison is instituted between them and the corresponding points of the right whale. One of the greatest peculiarities of the sperm whale, which strikes, at first sight, every beholder, is the apparently disproportionate and unwieldy bulk of the head; but this, instead of being, as might be supposed, an impediment to the freedom of the animal’s motion in his native element, is, on the contrary, in some respects very conducive to his lightness and agility. A great part of the bulk of the head is composed of a large, thin, membraneous case, containing, during life, a thin oil of much less specific gravity than water, below which again is the junk, which, although heavier than the spermaceti, is still lighter than the element in which the whale moves; consequently, the head is lighter than any other part of the body, and will always have a tendency to rise, at least so far above the surface as to elevate the nostril, or “spout-hole,” sufficiently for all purposes of respiration. In case the animal should wish to increase his speed to the utmost, the narrow anterior and inferior surface, which bears a resemblance to the cut-water of a ship, and which would, in fact, answer the same purpose to the whale, would be the only part exposed to the pressure of the water in front, enabling him thus to pass, with the greatest ease and celerity, through the boundless track of his wide domain. [Illustration: RIGHT WHALE.]