583 



CETACEA. 



A comparison of the ear-bone of Balama 

 Australis with that of Bal<ena Mysticetus cor- 

 roborates by differences, slight indeed, the dis- 

 tinction of species between them. 



" The cavity of the tympanum (a, a, Jig. 

 276) is lined with a membrane, which also 

 covers the small bones with their muscles, and 

 appears to have a thin cuticle. This membrane 

 renders the bones, muscles, tendons, &e. very 

 obscure, which are seen distinctly when that is 

 removed. It appears to be a continuation of 

 the periosteum, and the only uniting substance 

 between the small bones. Besides the general 

 lining, there is a plexus of vessels, which is 

 thin and rather broad, and attached by one 

 edge, the rest being loose in the cavity of the 

 tympanum, somewhat like the plexus choroides- 

 in the ventricles of the brain. The cavity, we 

 may suppose, intended to increase sound, pro- 

 bably by the vibration of the bone ; and from 

 its particular formation we can easily conceive 

 that the vibrations are conducted, or reflected, 

 towards the immediate organ, it being in some 

 degree a substitute for the external ear. 



" The external opening being smaller than in 

 any animals of the same size, the membrana 

 tympani is nearly in the same proportion. In 

 the Bottle-nose Whale, the Grampus, and Por- 

 poise, it is smooth and concave externally; but 

 of a particular construction on the inner sur- 

 face ; for a tendinous process passes from it to- 

 wards the malleus, converging as it proceeds 

 from the membrane, and becoming thinner till 

 its insertion into that bone. I could not dis- 

 cover whether it had any muscular fibres which 

 could affect the action of the malleus. In the 

 Piked Whale, the termination of the external 

 opening, instead of being smooth and concave, 

 is projecting, and returns back into the meatus 

 for above an inch in length, is firm in texture, 

 with thick coats, is hollow on its inside, and 

 its mouth communicating with the tympanum ; 

 one side being fixed to the malleus, by a part 

 similar to the tendinous process which goes 

 from the inside of the membrana tympani in 

 the others."* 



In the figure fjig.%76), which represents the 

 internal ear in the Balaena Mysticetus, the let- 

 ters c, d, e indicate the extent of the membrana 

 tympani, the letter e being placed on the part 

 which forms a convex projection into the tym- 

 panic passage : f shows the triangular ligamen- 

 tous process which attaches the handle of the 

 malleus (g) to the membrana tympani. This 

 connection between the membrane and the 

 ossicles of the tympanum is denied by Sir 

 Everard Home, who wrote a paper and pub- 

 lished two plates in support of his opinion.f 

 After quoting Mr. Hunter's description of the 

 attachments of the membrana tympani in the 

 Piked Whale, Sir Everard observes, " the fact 

 is, that there is no connexion whatever between 

 the membrana tympani and the malleus, as 

 will be explained ; but as that circumstance 

 forms the great peculiarity in the organ of this 

 species of Whale (Balana mysticetus, L.) 



* Hunter in Philos. Trans. 1787, p. 432. 

 t Philos. Trans. 1812, p. 88, p!s. I. and II. 



Fig. 27U 



Internal ear of the Mysticete Whale. 



I thought it right to quote what he hud stated 

 on this subject." So remarkable an anomaly 

 as an absence of any communication between 

 tl^e membrana tympani and the ossicula audi- 

 tus, would of itself, independently of our inte- 

 rest for the character of Hunter as an accurate 

 observer, have induced us to spare no pains to 

 test the conflicting statements with the facts 

 themselves ; fortunately in this instance the 

 preparations figured by Sir Everard are pre- 

 served ; we have carefully examined them, and 

 find the following to be the true structure of 

 the parts in question. The membrane marked 

 c in Sir Everard Home's second figure is con- 

 tinuous at d, with e the convex projection of 

 the membrana tympani ; whereas the edge of 

 the shadow is so strong in the figure as to 



o cp 



make it appear as if c and e were separate 

 membranes, as indeed Sir Everard de- 

 scribes them to be : they are, on the contrary, 

 parts of the same membrana tympani, the at- 

 tachment of which is extended inwards beyond 

 the circumference of the termination of the 

 bony meatus auditorius. The triangular liga- 

 ment fj which is common to all the Cetacea, is 

 attached not only to the plane portion of the 

 ear-drum, but to the whole of one side of the 

 convex portion which projects into the meatus, 

 and is affected by every motion of that part. 

 It is a thick opaque aponeurosis, and not, as it 

 is represented in the plate, a semitransparent 

 membrane passing clear over the convex part of 

 the drum. 



" A little way within the membrana tym- 

 pani, are placed the small bones, which are 

 three in number, as in the quadruped, mal- 

 leus (g), incus (h), and stapes ( i) ; but in 

 the Bottle-nose Whale (Hyperoodon) there is a 

 fourth, placed on the tendon of the stapedius 

 muscle. These bones are as it were suspended 

 between the bone of the tympanum, and that 

 of the immediate organ. 



" The malleus has two attachments, besides 

 that with the incus ; one close to the bone of 



