262 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
easy to answer. A preliminary difficulty to be encountered is the complex physio- 
logical character of the two organs ; and, apart from our imperfect knowledge of the 
physiology of the several functions assigned to each, and especially in the case of the 
internal ear of Fishes, a further difficulty is afforded by the total absence of any 
experimental evidence directly bearing on the functional significance of the Weberian 
ossicles. And, while we desire to emphasize the danger of making physiological 
deductions from facts of a purely anatomical nature, no other course has yet been 
adopted by previous writers on this subject, and, at present, this is the only one open 
to us ; consequently, any conclusions based upon data so frequently misleading and 
unreliable must partake rather of the nature of suggestions, and be accepted with 
considerable reserve. With the qualification rendered necessary by these considera- 
tions, some light may possibly be thrown on this difficult problem by a careful inquiry 
as to how far the Weberian ossicles, and the coadapted parts of the air-bladder and 
internal ear, ai’e anatomically fitted to act as subsidiary or accessory structures in 
connection with any of the several functions assigned to either the air-bladder or 
internal ear, while unsuited for association with others. By this means it may at 
least be possible to eliminate certain functions from any further consideration, and 
thereby considerably narrow the scope of future inquiry. 
With this object in view, we propose in this section of our paper to discuss (1) how 
far the function of the Weberian mechanism is conditioned by the anatomical structure 
of the air-bladder and internal ear ; (2) to which of the known functions of the air- 
bladder and auditory organ the Weberian ossicles are to be regarded as accessory 
structures ; and (3) the use and advantage of the Weberian mechanism to the Fish 
})Ossessing it. 
1. In all the Siluridse normales the air-bladder may be regarded as consisting of two 
intercommunicating, but physiologically distinct, portions — a posterior, represented by 
the two lateral compartments, which is indistensible and inelastic, and ahvays of 
gi-eater internal capacity ; and an anterior, which, on the contrary, is always more or 
less elastic and expansible, but of less internal capacity than the former. The 
distenslbillty of the anterior chamber, however, is by no means uniform in all direc- 
tions ; on the contrary, and for reasons already given, this portion of the bladder 
is absolutely inexpansible, except laterally at right angles to its antero-posterlor 
axis. From the mode in which the fibres forming the lateral walls of this chamber 
converge in each half of the dorsal wall and become inserted into the convex outer 
margin of the crescentic process of the tripus, it becomes still further obvious that it is 
only by inward or outward bulgings of the lateral walls that variations in the internal 
condition of the air-bladder are able to set in motion the series of Weberian ossicles. 
It is scarcely necessary to point out that by this restriction of the expansion or 
contraction of the anterior chamber to movements of its lateral walls, which alone 
* See pp. 93-'J5, 98, and 239-241. 
