ON THE ANATOMY OF FISHES. 
197 
naiTOw. The position of its dorsal margin coincides with the commencement of the 
posterior third of the length of the bladder, but from this point the septum inclines 
obliquely forwards, so that the relatively small lateral compartments are prolonged 
for some distance beneath the anterior chamber. The longitudinal septum [l.s.) 
separating the two lateral chambers also extends forwards, gradually diminishing in 
height along the posterior face of the inclined transverse septum. The lateral edges 
of the transverse septum are recurved and directed backwards for a short distance 
parallel to each other and to the longitudinal septum. Between these recurved 
margins and the prolongation of the longitudinal septum on to the posterior face of 
the oblique transverse septum, the lateral compartments extend forwards beneath the 
anterior chamber in the form of two cul-de-sacs, which finally become obliterated 
when the two septa blend with the ventral wall of the bladder. The anterior 
chamber (a.c.), like the lateral compartments (l.c.) has comparatively thin walls, 
and for a limited portion of their extent its lateral walls are in close relation with the 
superficial skin. The anterior wall of the chamber is strengthened by a strong, 
tendinous transverse membrane which has the usual skeletal attachments laterally 
and dorsally, and in the median line is firmly inserted into the lateral and ventral 
margins of the subvertebral process. Both the anterior and lateral chambers have 
perfectly smooth inner surfaces, the latter being devoid of even the rudiments of 
secondary transverse septa. In the general disposition and skeletal attachments of 
the fibres forming the walls of the anterior chamber, Flotosus very closely resembles 
Macrones. 
The scaphium has ascending, condylar, and spatulate processes. The intercalarium 
is a thin, discoidal nodule of bone in the interossicular ligament. The anterior and 
articular processes of the tripus are normal, but the crescentic process (figs. 82, 83, 
r.c.) has but a feebly marked oblique ventral ridge, and is somewhat hook-shaped, 
with an acutely-pointed posterior or inner extremity. 
The cavum sinus imparis and its atrial cavities are perfectly normal, and the same 
may be said of the correlated portions of the membranous labyrinth. 
As in Clcirias the mesonephros gives off a characteristic lateral outgrowth on each 
side which occupies a recess in the lateral musculature of the trunk, between the 
external skin and the outer wall of the adjacent lateral compartment of the air- 
bladder. 
Plotosus anguillaris. 
This species differs in no essential respect from the preceding. The air-bladder is 
perhaps somewhat broader and deeper in proportion to its length, and its walls much 
thinner. The forward extension of the lateral chambers beneath the anterior com- 
partment is even more marked than in P. canius, inasmuch as they reach the ventral 
margin of the interior wall of the bladder. From an examination of several young and 
half-grown examples of this species, it is obvious that the air-bladder does not always 
