VOL. LXXVII.] PHILOSOPHICAL TANSACTIONS. 341 



easily assign a reason why there should be no projecting ear, as it would inter- 

 fere with progressive motion; but the reason why it is not formed as in birds, is 

 not so evident; whether the percussions of water could be collected into one 

 point as air, I cannot say. The tympanum is constructed with irregularities, so 

 much like those of an external ear, thai I could suppose it to have a similar 

 effect. 



The external opening begins by a small hole, scarcely perceptible, situated on 

 the side of the head a little behind the eye. It is much longer than in other 

 animals, in consequence of the size of the head being so much increased beyond 

 the cavity that contains the brain. It passes in a serpentine course, at first hori- 

 zontally, 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 irregular and united together by cellular membrane, 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 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 general 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 immediate organ 

 and the tympanum. 



The immediate organ is, in point of situation to that of the tympanum, su- 

 perior and internal, as in the quadruped. The tympanum is open at the an- 

 terior end, where the eustachian tube begins. The eustachian tube opens on 

 the outside of the upper part of the fauces: in some higher in the nose than 

 others; highest I believe in the porpoise. From the cavity of the tympanum, 

 where it is rather largest, it passes forwards and inwards, and near its termi- 

 nation appears very much fasciculated, as if glandular. The eustachian tube 

 and tympanum communicate with several sinuses, which passing in various di- 

 rections surround the bone of the ear. Some of these are cellular, similar to 

 the cells of the mastoid process in the human subject, though not bony. There 

 is a portion of this cellular structure of a particular kind, being white, liga- 

 mentous, and each part rather rounded than having flat sides*. One of the 

 sinuses passing out of the tympanum close to the membrana tympani, goes a 

 little way in the same direction, and communicates with a number of cells. The 

 whole function of the eustachian tube is perhaps not known ; but it is evidently 

 a duct from the cavity of the ear, or a passage for the mucus of these parts ; 



* These communications with the eustachian tube may be compared to a large bag on the bases of 

 the skull of the horse and ass, which is a lateral swell of the membranous part of the tube, and. 

 when-distended will contain nearly a quart. — Orig. 



