116 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
Internally the bladder is divided into spacious anterior and lateral chambers by 
strong primary transverse and longitudinal septa (fig. 34, ts., Is.), while each lateral 
compartment is also sub-divided into a series of transversely arranged inter-com- 
municating cavities by six incomplete secondary transverse septa (fig. 34, ts.'). 
Strong root-like bundles of fibres radiate from the dorsal edges of the secondary septa 
into the dorsal Avail of the bladder, and still further contribute to the peculiar 
camerated structure of that organ. The lateral portions of the primary transverse 
septum remain nearly vertical, but its mesial part is inclined obliquely forwards before 
it finally becomes continuous with the ventral wall ; hence the ventral edge of the 
septum is somewhat V-shaped, with the apex directed forwards, while the lateral 
compartments and the longitudinal septum which separates them are prolonged 
forwards for some distance ventrad to the inclined septum and to the anterior 
chamber."^ The dorsal edge of the transverse septum is firmly inserted into the 
oblique ridges on the lateral surfaces of the centrum of the fifth vertebra, and also 
into their prolongations on to the ventral surfaces of the contiguous transverse 
processes (fig. 32). 
The tunica externa of the anterior wall of the bladder is divisible into two strata, 
of wdiich the outer and thicker is attached in the median line by its dorsal edge to 
the ventral and lateral surfaces of the anterior portion of the complex centrum, and. 
also to the radial nodules and dorsal laminae, but externally to this on each side the 
outer stratum, instead of extending into the dorsal wall and becoming connected 
with the corresponding tripus, separates from the inner and is inserted by its dorsal 
margin into the anterior edge and distal extremity of the transverse process of the 
fourth vertebra. In the lateral walls of the anterior chamber the fibres composing 
this stratum pursue the usual curvilinear course as they are traced into the dorsal 
wall, where they converge in the form of triangular sheets to their insertion into the 
convex outer margins of the crescentic processes of the tripodes (fig. 34, tr.c., o.st.). 
The sheets are somewhat narrower than usual, and have a slightly concave inner 
margin, while the thin medio-dorsal area of the tunica externa, which invests and is 
attached to the ventral and lateral surfaces of the complex and fifth vertebral centra, 
is relatively much Avider than in most other Siluroids ; hence the surfaces of these 
centra and the roots of their transverse processes are readily seen through the thin 
area Avhen the tunica interna has been removed. The inner and much thinner of the 
tAvo strata of the tunica externa of the anterior AA-all divides in the median line 
beneath the complex centrum, and on each side the more mesially situated fibres are 
inserted dorsally into the inner margin and v’entral surface of the root of the 
crescentic process of the tripus ; laterally to this point the fibres of the inner stratum, 
Avhich are vertically disposed, describe an iiiAA^ard curvature towards the tripus as 
they extend into the dorsal wall, and eventually become inserted into the coiiAmxity 
of its crescentic process (fig. 34, in.st.). From the antero-lateral and lateral A\nlls of 
* In fig. .34 the right half of the transverse septum has been partially removed. 
