ON THE ANATOMY OF PISHES. 
lOO 
posterior walls of each sac seemed to be closely attached to the corresponding 
margins of the bony recess, in which the sac itself is partially enclosed, while the 
inner wall is similarly adherent to the lateral surface of the complex centrum, to the 
triangular ventral process, and to the dorsal lamina. The rigid skeletal attachments 
of the two air-sacs are substantially similar to those of the similarly modified air- 
bladders of Bagarius and Glyptosternum, and, probably, as we shall point out more 
particularly in our description of the last-mentioned genus, are capable of strict 
comparison with the attachments of a normal anterior chamber, or, at least, present 
only such differences as are necessitated by the constriction of the bladder into two 
distinct lateral divisions. Although obvious enough elsewhere, we could detect no 
definite disposition of fibres in the dorsal wall of either of the two air-sacs, neither 
could we trace the usual convergence of fibres from the antero-lateral and outer walls 
towards the crescentic process of the tripus ; in fact the dorsal wall of both sacs 
appeared to be represented solely by an extremely thin stratum of connective tissue. 
We are inclined to regard this stratum as belonging to the inner tunic, the tunica 
externa of the dorsal wall having completely atrophied. We were unable to discover 
any trace of an investing epithelium, but failure in this respect was probably due to 
the ill-preserved condition of the specimen. It is, of course, possible that the apparent 
degeneration of the proper fibrous portion of the dorsal wall may also be the result of 
the same cause, but from the undoubted existence of similar structural lesions in 
other abnormal Siluridse we prefer, provisionally at any rate, to regard this condition 
as normal so far as Akysis is concerned. 
The possibility that structural defects in the connection of the walls of the 
air-bladder with the tripodes might be correlated with the existence of similar 
retrogressive modifications in those portions of the internal ear which are specially 
associated wuth the Weberian mechanism, induced us to make a careful examination 
of the cavum sinus imparis and its contents. The cavum itself and its atrial 
diverticula appeared to be perfectly normal, but relatively small in point of size. 
A ductus endolymphaticus was present, but of a sinus endolymphaticus we could 
find no trace whatever. How far our inability to discover the latter structure was 
due to the condition of the specimen, or to its real absence, we are unable to say, but 
while admitting the possibility of the former alternative, we must point out that the 
latter receives some support from the almost certain suppression of the sinus in 
other and in many respects similarly abnormal Siluridse. 
Of the Weberian ossicles the scaphium has no ascending process, but is otherwise 
normal ; its condyle is at the hinder extremity of the spatulate process, which, 
anteriorly, has the usual relations to the external atrial aperture of its side. The 
intercalarium is reduced to a very small nodule, imbedded in the interossicular 
ligament, having lost both its ascending and horizontal processes. We could find no 
trace of claustra. The tripus is a triradiate and very slender ossicle (fig. 29, tr.). 
The anterior process is directed forwards and a little inwards as it passes to its 
