CETACEA. 



587 



mediate organ (or labyrinth) and the tym- 

 panum. 



" The immediate organ is, in point of situa- 

 tion to that of the tympanum, superior and in- 

 ternal, as in the quadruped. The tympanum 

 is open at the anterior end, where the Eusta- 

 chian 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 tym- 

 panum, where it is rather largest, it passes 

 forwards and inwards, and near its termination 

 appears very much fasciculated, as if glan- 

 dular. (A probe passes through the Eusta- 

 chian tube in the figure, showing its nasal ter- 

 mination at d.) 



" The Eustachian tube and tympanum com- 

 municate with several sinuses, which passing 

 in various directions surround the bone of the 

 ear. Some of these are cellular, similar to the 

 cells of the mastoid process in the human sub- 

 ject, although not bony. There is a portion of 

 this cellular structure of a particular kind, being 

 white, ligamentous, and each part rather round- 

 ed than having flat sides.* 



" One of the sinuses passing out of the tympa- 

 num close to the membrana tympani, goes a 

 little way in the same direction, and commu- 

 nicates 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 ; the external 

 opening having a particular form would incline 

 us to believe, that something was conveyed to 

 the tympanum. 



" The bony part of the organ is very hard 

 and brittle, rendering it even difficult to be cut 

 with a saw, without its chipping into pieces. 

 That part which contains the immediate organ 

 is by much the hardest, and has a very small 

 portion of animal substance in it; for when 

 steeped in an acid, what remains is very soft, 

 almost like a jelly, and laminated. The bone 

 is not only harder in its substance, but there is 

 on the whole more solid bone than in the cor- 

 responding parts of quadrupeds, it being thick 

 and massy. 



u The part containing the tympanum is a 

 thin bone, coiled upon itself, attached by one 

 end to the portion which contains the organ ; 

 and this attachment in some is by close contact 

 only, as in the Narwhale ; in others, the bones . 

 run into one another, as in the Bottle-nose and 

 Piked Whales ( Hyperoodon and Balanop- 

 tera). 



" The concave side of the tympanum is 

 turned towards the organ, its two edges being 

 close to it ; the outer is irregular, and in many 

 only in contact, as in the Porpoise : while in 

 others the union is by bony continuity, as in 

 the Bottle-nose Whale (Hyperoodon), leaving 

 a passage on which the membrana tympani is 



* ' 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." 



stretched, and another opening, which is the 

 communication with the sinuses. 



" The surface of the bone containing the im- 

 mediate organ (the petrous bone, p, Jig. 269) 

 opposite to the mouth of the tympanum is very 

 irregular, having a number of eminences and 

 cavities." 



According to the Baron Cuvier* the petrous 

 bone in the Delphinida is permanently lodged 

 between the temporal and contiguous parts of 

 the occipital bone; it forms the upper and 

 inner part ; the tympanum the lower and outer. 

 The petrous bone is brittle and very thick. It 

 has a larger portion, an irregular ellipsoid, 

 which gives attachment to the tympanum by 

 its outer surface, and which contains the three 

 semicircular canals ; and another smaller por- 

 tion in the form of a quarter of a sphere, which 

 is separated from the first by a pretty deep de- 

 pression, and is occupied internally by the 

 cochlea. The acoustic nerves enter by fora- 

 mina at the bottom of the depression. 



The tympanum is formed by a thick bony 

 plate folded longitudinally, so as to form a 

 canal, open anteriorly, whence is continued the 

 Eustachian tube. It is closed behind, where 

 it assumes a bilobate figure, and adheres above 

 this part to the outer and posterior part of the 

 petrous bone by a rough process, which is 

 firmly wedged in, but does not anchylose soon. 

 It adheres to it also by a part of the external 

 margin, and it is between these two points of 

 adhesion that we find the very irregular opening 

 of the tympanum. The internal margin leaves 

 a long interval between it and the petrous bone. 

 Beneath the bilobate portion of the tympanum 

 the styloid process passes, which is attached 

 immediately behind it by ligaments to the de- 

 scending plate, which represents the mastoid 

 process. 



The bone of the ear of the Cachalot displays 

 great relations with that of the Dolphins, 

 only the tympanum is shorter and less lobated 

 behind. 



The bone of the ear in the Balanida differs 

 from that of the Delphinida: by the enormous 

 thickness of the tympanum (a, fig. 276), espe- 

 cially at the inner side. This tympanum is a 

 little more closed anteriorly, but leaves between 

 it and the os petrosum (b) on the inner side a 



Proportionally shorter and wider interspace, 

 t is not bilobed posteriorly. 



The petrous bone is of a very irregular shape 

 and knotty surface ; it gives off two large rough 

 processes, of which one is situated behind and 

 a little above, and articulates with a corre- 

 sponding process of the tympanum, is wedged 

 between the temporal and lateral occipital 

 bones; and the other, situated anteriorly and 

 below, is articulated by a squamous suture 

 with the part of the temporal which descends 

 to furnish the articulation of the lower jaw. 

 This second process, which in the BalteruB is as 

 large as the other, is very small in the Bala- 

 noptera ; nevertheless the ear-bone of the Ba- 

 Isenae is fixed more solidly to the cranium than 

 that of the Delphini. 



* Oss. Foss. vol. v. pt. i. p. 300. 

 2 Q 2 



