ON THE ANATOMY OF FISHES. 
147 
— a fact which supports our suggestion that this ridge is in part the equivalent of the 
dorsal lamina in other Siluridae. In a precisely similar manner the anterior wall is 
firmly adherent to the decurved anterior margin of the transverse process of the 
fourth vertebra. The inner wall of the air-sac is also attached to the dorsal ridge, 
where the latter traverses the side of the complex centrum. The only other point 
at which each air-sac is attached to a rigid portion of the skeleton is about the centre 
of its ventral wall, where the latter blends with its investing superficial coat, and 
both become firmly attached to the triangular outgrowth from the ventral ridge. 
The straight posterior process of the tripus lies near the inner extremity of each 
air-sac in relation with the imperfect dorsal wall of the latter, but we were only able 
to detect a few fine-scattered fibres extending from the outer margin of the process 
obliquely outwards and forwards towards the antero-lateral and anterior walls of the 
sac. These fibres appear to be all that represent the thick triangular sheet of fibres 
which is so characteristic of each half of the dorsal wall of a normally developed 
anterior chamber, and are practically confined to rather less than the anterior half of 
the dorsal wall of the sac. In the posterior half of the dorsal wall we could detect 
only a thin stratum of connective tissue, which probably belongs to the tunica interna, 
although we could not with certainty detect any epithelium on its inner surface. No 
radial fibres could be made out. 
The tripus (fig. 54, tr.), is a simple triradiate ossicle, with a long anterior process 
(tr. a.), which is connected with the scaphium by a relatively short interossicular 
ligament, a tapering articular process [tr. cir.), and a posterior division (tr. c.) which 
remains in a straight line with the anterior process, and tapers to a point at its hinder 
extremity without describing the normal crescentic curvature. The scaphium has no 
ascending process, but its horizontal spatulate portion terminates posteriorly in a 
spherical condyle. The intercalarium is a very small nodule of bone imbedded in 
the interossicular ligament. Claustra seem to be entirely absent. 
The cavum sinus imparis and the atrial cavities are extremely small, but other- 
wise normal. We had no difficulty in detecting a transverse ductus endolymphaticus, 
but a most careful examination failed to reveal any trace of a sinus endolymphaticus. 
Glyptosternum platypogon. 
Under the name of Pimelodus platypogon, Cuvier and Valenciennes (8) describe 
this Siluroid as being devoid of an air-bladder. In a paper published in the Lin- 
nean Society’s ‘ Journal,’ vol. 13, Day, in referring to Glyptosternum telchitta remarks, 
“I cannot detect any air-vessel in this species.” In 1871 (‘ Proc. Zool. Soc. Lon.,’ p. 
289), Day corrected his previous statement, and in again referring to the same species 
tersely describes the air-bladder as consisting of “two rounded lateral portions, very 
thin, and entirely enclosed by bone.” In a later paper in the same year (‘Proc. 
Zool. Soc.,’ 1871, p. 714), he again refers in equally brief terms to Glyptosternum as 
having “ an air-vessel in two rounded lateral portions, and enclosed in bony capsules,” 
u 2 
