580 



CETACEA. 



" The crystalline humour (d) resembles that of 

 the quadruped ; but whether it is very convex 

 or flattened, I cannot determine; those I have 

 examined having been kept too long to pre- 

 serve their exact shape and size. The vitreous 

 humour adheres to the retina at the entrance 

 of the optic nerve. The optic nerve (f ) is very 

 long in some species, owing to the vast width 

 of the head."* 



The crystalline lens is of a spherical form, 

 but slightly flattened anteriorly : it is inclosed 

 in a strong and dense capsule, and is placed 

 at a very small distance from the cornea, so 

 that it diminishes the space for the aqueous 

 humour, while it increases that for the vitreous; 

 this exists in a greater degree than is shown in 

 the subjoined figure, as Soemmering, from 

 whose work ' De oculorum sectione horizon- 

 tali' the figure is taken, himself allows. From 

 the peculiar colour and eccentric position of 

 the nucleus of the lens in the Whale's eye, in 

 which it is of a dark colour, and placed in the 

 posterior half of the lens, we are led to suspect 

 that the section of the lens in Soemmering's 

 plate is imaginary.] 



Ear. The ear is without any external con- 

 cha ; no doubt a sphincter has the office of 

 closing the entrance of the auditory canal, to 

 preserve the tympanum, which some call fi- 

 brous, and others cartilaginous, from the 

 contact of the water. The Eustachian tube 

 exists according to some anatomists, others 

 deny it. The senses of sight and hearing, not- 

 withstand ing their apparent imperfection, appear 

 to be endued with great delicacy. Whale- 

 catchers assert that Whales, Cachalots, &c. see 

 and hear at a great distance, and that, in order 

 to approach them, many precautions are neces- 

 sary ; otherwise these animals would avoid 

 them by a sudden retreat, and it would become 

 necessary to recommence the long and labo- 

 rious chase. We ought, nevertheless, to add 

 that Scoresby, who speaks of the delicacy 

 of hearing of the Whales, states that they 

 remain insensible to the noise of the report of 

 a cannon. 



[For the most accurate and philosophical 

 description of the Organ of Hearing in the 

 present tribe we again recur to Hunter's ad- 

 mirable paper on the organization of the 

 Cetacea. He observes, that " the ear is con- 

 structed much upon the same principle as 

 in the quadruped ; but as it differs in several 

 respects, which it is necessary to particularize, 

 to convey a perfect idea of it the whole should 

 be described. As this would exceed the limits 

 of this paper, I shall content myself with a 

 general description, taking notice of those ma- 

 terial points in which it differs from that of the 

 quadruped. 



" This organ consists of the same parts as in 

 the quadruped ; an external opening, with a 

 membrana tympani, and Eustachian tube, a 

 tympanum with its processes, and the small 

 bones. 



" There is no external projection forming a 

 funnel, but merely an external opening. We 



* Philos. Trans. 1787, p. 440. 



can easily assign a reason why there should be 

 no projecting ear, as it would interfere with 

 progressive motion ; but the reason why it is 

 not formed as in birds, is not so evident ; whe- 

 ther the percussions of water could be collected 

 into one point as air, I cannot say. The tym- 

 panum is constructed with irregularities, so 

 much like those of an external ear, that I could 

 suppose it to have a similar effect. 



" The external opening begins byasmall hole, 

 (a, fig. 275), scarcely perceptible, situated on 



Fig. 275. 



Organ of Hearing, Porpesse. 



It 



the side of the head a little behind the eye. 

 is much longer than in other animals, in con- 

 sequence, of the size of the head being so much 

 increased beyond the cavity that contains the 

 brain. It passes in a serpentine course (6), at 

 first horizontally, then downwards, and afterwards 

 horizontally again, to the membrana tympani, 



where it terminates. In its whole length it 



is 



composed of different cartilages, which are irre- 

 gular and united together by cellular mem- 

 brane, so as to admit of motion, and probably 

 of lengthening or shortening, as the animal is 

 more or less fat. 



" The bony part of the organ (r, c) is not so 

 much inclosed in the bones of the skull as in the 

 quadruped, consisting commonly of a distinct 

 bone or bones, closely attached to the skull, 

 but in genera! readily to be separated from it ; 

 yet in some it sends off, from the posterior 

 part, processes which unite with the skull. It 

 varies in its shape, and is composed of the im- 



