ON THE ANATOMY OF FISHES. 
235 
and possibly at the same time less compressible, by the formation of a variable 
number of secondaiy transverse septa {e.g., Macrones), which incompletely subdivide 
each chamber into a series of transversely arranged, intercommunicating spaces. The 
support which these septa afford to the walls of the lateral chamber is, in some cases, 
strengthened by root-like bundles of fibres which grow out from the dorsal and 
ventral margins of the septa, and extend into the corresponding walls of these 
chambers. Occasionally the excessive development of these septa, and their union 
by root-like bundles of fibres which pass between their opposed surfaces, may lead to 
the formation of a thick trabecular network of fibrous columns or bands, and to the 
partial obliteration of the cavities of the two chambers {Pangasius). 
The width of the primary transverse septum, formmg the posterior wall of the 
anterior chamher, varies greatly in different Siluroids. In some {e.g., Auchenoglanis) 
the septum is co-extensive with the width of the air-bladder, although contracted 
dorsally to admit of the lateral chambers communicating with the anterior chamber ; 
in others {e.g., Callichrous, Cryptopterus) the septum is reduced to the condition of a 
narrow, but stout, column-like aggregation of fibres. 
In many members of this group the primary transverse septum, and more particu- 
larly its median portion, is more or less oblique, and in some extremely so. This 
obliquity of the septum has the effect of causing the lateral chambers and the longi- 
tudinal septum to extend forwards to a varying extent, ventrad to the inclined 
septum, and consequently to overlap the anterior chamber along the greater part of 
its ventral surface. 
Caecal appendages to the anterior and lateral compartments are not uncommon. 
The anterior chamber may have small anterior cmca {Maa'ones aor), or much smaller 
antero-lateral caeca {Osteogeniosus). In the former case the caeca bulge forwards into 
goblet-shaped cavities excavated In the substance of the inferior processes of the post- 
temporal bones. Lateral caeca are sometimes present, and may either take the Ibrm 
of large funnel-shaped structures, which extend the whole length of the abdominal 
cavity and are entirely free from internal subdivisions {Rita), or may occur as small 
forwardly directed outgrowths, subdivdded internally by a network of fibrous bundles, 
and communicating with the anterior chamber by a number of slit-like orifices in its 
lateral walls {Platy stoma). The lateral compartments are frequently either con- 
stricted or prolonged into a posterior cmcal appendage. I'liis may be a longer or 
shorter tubular, or a slightly oval structure, and confined to the abdominal cavity 
{Pangasius Buclianani, Bagroides melanopterus), or a long tapering tubular struc- 
ture, which, after traversing the abdomen, extends for some distance along the right 
side of the tail between the haemal arches and the lateral musculature {e.g., Crypto- 
pterus micronema and C. micropogon). In some cases the posterior cmcum is very 
large, and in shape an elongated oval body {Pangasius djambol, Malapteruims 
electricus), or it may be flattened and leaf-like {Pangasius rnacronema). In one 
instance {Oxydoras) it is very rudimentary. The existence of a pair of rudimentary 
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