ON THE ANATOMY OF FISHES. 
Ill 
posterior cardinal veins, or of the ventral outgrowths from the superficial ossifications 
which are so conspicuous a feature in Bagarius and Glyptosternum, and to a less 
extent in Ahysis also. 
The stem and ascending process of the post-temporal are very similar to those of 
Ahysis. The inner surface of the stem forms the outer boundary, and the recurved 
distal portion of the modified transverse process the inner and anterior walls, of the 
socket for the head of the clavicle [cl.). There is no trace of an inferior limb, in fact, 
this process seems, as it were, to have been crowded out by the abutment of the 
anterior margin of the transverse process against the posterior and opisthotic plates 
of the exoccipital. 
The air-bladder differs in no essential feature from that of Ahysis, and, as in the 
latter Siluroid, is completely constricted into two small laterally placed air-sacs, 
which occupy the concavities of the modified transverse processes of the fourth 
vertebra (fig. 30, a.s.).^ There is no communication between the two sacs, neither is 
there a ductus pneumaticus. As regards the skeletal attachments of the air-bladder, 
the degenerate condition of its dorsal wall, and the apparent atrophy of the sinus 
endolymphaticus, there is also an extremely close resemblance between the two 
genera, and this agreement further extends in almost every detail to the condition of 
the Weberian ossicles. 
It must be admitted that while there are several features in connection with the 
air-bladder in Acrochorclonichthys and Ahysis which favour the belief that its structural 
peculiarities are due to the degeneration of an originally normal bladder, our results 
are not quite conclusive on this point. Mere reduction in the size of the air-bladder 
is obviously not sufficient to prove the uselessness of its connection with the auditory 
organ through the Weberian mechanism, but structural imperfections in either 
organ, or in the connecting ossicles, would be decisive. That the two air-sacs are 
distinct we have no doubt, and the total atrophy of the ductus pneumaticus seems 
equally certain, but more definite information as to the presence or absence of the 
sinus endolymphaticus, and as to the condition of the dorsal walls of the air-sacs and 
their relations to the tripodes, is desirable before it can be positively affirmed that 
the air-bladder and Weberian mechanism are physiologically useless in these genera. 
Our failure to find a sinus endolymphaticus may be due, as we have already pointed 
out, either to its absence, as we suggest, or to the imperfect preservation of our 
specimens, but if the former alternative be true, our tentative conclusions on other 
uncertain points would receive strong support, for if the physiological connection of 
the Weberian ossicles and the air-bladder were lost through the partial or complete 
atrophy of the dorsal walls of the air-sacs, it would be reasonable to anticipate the 
existence of similar retrogressive changes in that part of the auditory organ which is 
specially related to those structures. In subsequently dealing with two other 
abnormal Siluroids [Bagarius and Glyptosternum) we shall point out that they 
* The dimensions of each sac were : length, 2 3.3 mra., width, l o ram. 
