124 
rROFRftSORR T. W. BRTDGK AND A. C. HADDON 
for the distal two-thirds not only downwards but also backwards towards the 
posterior margin. The posterior edge of the process is also decurved, but to a some- 
what less extent than the former. By these modifications each process forms the 
outer walls of a flask-shaped recess which is open posteriorly and distally in the dry 
skeleton, but closed behind by a tough fibrous membrane, and at the distal extremity 
by the lateral cutaneous area of its side in the fresh specimen. The recess is slightly 
expanded distally, somewhat contracted towards the centre, and again expanded at 
the root of the process into a relatively spacious cavity for the reception of the inner 
lateral cmcal portion of the air-bladder. The decurved anterior margin of the process 
articulates by means of a facet on its anterior face with the inferior limb of the post- 
temporal {2')t.i.), while the distal edge of its recurved portion forms part of the inner 
wall of the socket for the clavicle (cl.s.), the outer wall being formed by the greatly 
elongated post-temporal stem (pf.s.). The recurved portion also forms the lower lip 
of the distal opening of the enclosed recess. The transverse process of the fiftli 
vertebra is much larger than any of the normal processes, and for the whole extent 
of its anterior margin is suturally united to the preceding process The trans- 
verse process of the next vertebra which is much shorter and thicker, is widely 
separated from the foregoing and carries the first rib {r.'). 
As the result of its extremely degenerate condition the air-bladder is very curiously 
modified. It consists of a median portion (a.h.) which is flattened, leaf-like, and 
apparently solid, and of two lateral out-growths on each side. Of these out-growths 
the outer lateral one (o.I.) is also thin and solid, and, after curving forwards and 
inwards like a broad crescent, ultimately contracts rather abruptly into a slender 
tubular pm'tion which bends upwards and inwards and ends blindly near the ventral 
wall of the saccus paravertebralis in the substance of the anterior lymphoid portion 
of mesonephros. The inner lateral out-growth (in.l.), on the contrary, is a hollow 
and relatively spacious crecum, with fairly thick walls, which, after leaving the median 
part of the bladder, curves round the lateral surface of the complex centrum in the 
oblique groove to which reference has already been made, and finally enters the deep 
bony recess on the ventral side of the root of the modified transverse process where it 
slightly expands and becomes connected by its dorsal and inner walls with the tripus 
and the radial nodule respectively. No portion of the air-bladder extends into the 
distal two-thirds of either recess. At its blind anterior extremity the walls of the inner 
lateral cmcum are much thinner than elsewhere, but its cavity is practically distinct 
from that of its fellow of the oj)posite side. With the exceptions above mentioned, 
the whole of the air-bladder is apparently solid althougli denser externally than 
internally. The solidity of the organ is, however, really due to the almost complete 
obliteration of its original cavity by the development of a dense internal reticulum of 
anastomosing fibrous bundles. The median portion of the bladder, and especially the 
* It is possible that the outer lateral cnpcum is a degenerate remnant of the antero-lateral caaca of 
other Siluridae (e.g., Platy stoma). 
