132 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
and the expanded first interspinous bone, respectively, renders the connection between 
the two structures exceptionally rigid. 
The post-temporal is normal in shape, and in its relations to the skull and to the 
transverse processes of the fourth vertebra. The inferior limb of the bone articulates 
with a stout projection from the lateral surface of the basioccipital (fig. 47, The 
cleft in the stem of the post-temporal to form the clavicular socket is unusually deep 
(cl.s.). There are no post-temporal plates. 
The air-bladder has the usual cordate shape, but its walls are exceptionally stout 
and rigid (fig. 48). Its anterior wall is traversed by a deep median vertical groove, 
due to the impression of the sub vertebral process (sv.p.). As in most other normal 
Siluridos, the cavity of the bladder is subdivided into an anterior (a.c.) and two 
lateral chambers (l.c.) by the usual A -shaped disposition of the primary transverse 
{t.s.) and longitudinal (Is.) septa; and the cavity of each lateral compartment is 
further subdivided by several secondary transverse septa {t.s.'). Strong buttresses of 
fibres pass from both faces of the secondary septa, and also from the posterior face of 
the principal transverse sejitum, and extend into the adjacent portions of the ventral 
wall of the two lateral compartments. The primary transverse septum (t.s.) is very 
thick, and inclines obliquely downwards and forwards from its dorsal attachment to 
the skeleton to its junction with the ventral wall of the bladder. Here, as in 
Platystoma, the obliquity of the septum has the effect of causing the lateral 
compartments to extend forwards for some little distance beneath the anterior 
chamber. The dorsal margin of the septum is firmly attached to the posterior and 
lateral edges of the superficial ossifications where the latter invest the body of the 
fifth vertebra, and, externally to this, to the ventral surfaces of the transverse 
processes of the same vertebra. The mesial portion of the anterior face of the septum 
is thickened into two stout, forwardly projecting, parallel ridges, which are continued 
dorsally to the skeletal attachments of the septum ; ventrally the ridges extend 
downwards, and, at the same time, curve forwards along the inner surface of the 
ventral wall of the anterior chamber, while still retaining their parallel relations 
{r.s.y ^ ; from the ventral wall the two ridges again extend dorsal wards on the poste- 
rior face of the anterior wall, where the fibres of which they are composed, with the 
addition of the remaining fibres of the median portion of the anterior wall, diverge in 
the form of two bundles (anterior pillars), and pass, one on each side of the complex 
centrum, to the lateral surfaces of which and to the radial nodules they eventually 
become attached. In the anterior wall the vertically disposed ridges are evidently 
the result of a special concentration of the vertical fibres, which normally, as in 
Macrones, form the inner stratum of the tunica externa in that region, while the 
* lu fig. 48 only the lateral portions of the ventral wall of the anterior chamber have been removed, 
the median portion remaining intact, except that an oval window has been cut in it in order to show the 
parallel ridges on its inner surface. The same figure also shows the obliquity of the primary transverse 
septum, and the forward extension of the two lateral compartments. 
