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PROFESSORS T. W. BRIDGE AND A. C. H ADDON 
air-bladder in this group is in the form of two simple, pyriform or globose, thin- 
walled, laterally placed air-sacs, which are either distinct or connected by an inter- 
mediate tubular portion {e.g., Glyptosternum, Euclyptosternum, Cetopsis, Bagarius. 
Ahysis, Acroclwrdonichthys, Clarias, Saccohranchus, and Pimelodus pulcher). 
The skeletal attachments of the air-bladder to rigid portions of the skeleton 
exhibit as a rule much the same extent and kind of variation as we have already 
described in the case of the anterior chamber of the more normal Siluroids. In such 
forms as possess rudiments of lateral chambers, and of primary transverse and longi- 
tudinal septa, the attachments of the air-bladder to the anterior vertebrae are 
perfectly normal, and even in many genera where those structures are entirely 
wanting the skeletal attachments are often very similar to those of the normal 
Siluridae. Thus in those cases in which the bladder is represented by two distinct or 
mesially intercommunicating air-sacs, the dorsal attachment of the primary transverse 
septum in the normal organ is represented either by the attachment of the dorsal 
edge of the median portion of the posterior wall to the ventral surface and sides 
of the complex centrum {e.g., Pimelodus pulcher), or by a similar attachment of the 
corresponding margin of the posterior wall of each lateral air-sac to the hinder 
margin of the transverse process of the fourth vertebra, or to the ventral surface of 
the corresponding process of the fifth vertebra in those cases in which the latter 
process participates in the formation of the osseous recesses {e.g., Bagarius, Clarias, 
Glyptosternum, &c.). The median and tubular portion of the air-bladder, when 
present, is always thin- walled, and its firm connection with the ventral surface of the 
complex centrum evidently corresponds to the skeletal attachment of the thin medio- 
dorsal portion of a normal anterior chamber {e.g., Clarias). The same remark will 
apply also to such cases in which the median portion of the constricted air-bladder is 
represented by a band of fibrous tissue, without any lumen, passing from one air-sac 
to the other, and firmly attached to the ventral surface of the complex centrum 
{e.g., Bagarius, Glyptosternum, and others). Whether the median tubular portion of 
the air-bladder be present or absent, the inner portion of the anterior wall of each 
air-sac is almost invariably attached to the contiguous lateral surfaces of the complex 
centrum, or to the radial nodule, or even to both, after the fashion of the anterior 
pillars of the normal bladder. Occasionally also, as in such normal forms as Arius 
and its allies, the outer stratum of the anterior wall of each air-sac may be dorsally 
connected with the decurved anterior margin of the transverse process of the fourth 
vertebra {e.g., Bagarius, Glyptosternum, and Akysis). As a rule, however, in the 
limited number of instances where the air-bladder is almost completely surrounded 
by its osseous capsules, the rigid skeletal attachments of the former are not so obvious 
as in those cases in which the bony investment is but partial {e.g., Callomystax, 
Cetopsis, &c.). Broadly speaking it may be affirmed that reduction in the size of the air- 
bladder, and its structural degeneration in other respects, do not to any great extent 
