88 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
inner surfaces of tlie lateral cutaneous areas, but more posteriorly the side walls 
contract from the external skin and the lateral musculature of the trunk, and, with 
the posterior wall, become closely embraced by the lateral and median posterior lobes 
of the mesonephros (fig. 18, mph.). 
Immediately in front of the air-bladder, and closely moulded to the convexity of its 
anterior -wall, the so-called head-kidney,"* consisting of two lateral lobes and a thin 
transversely disposed connecting lobe, may be seen through the thin peritoneal layer 
which invests its ventral surface. Each lateral lobe occupies a recess between the 
inferior limb of the post-temporal in front, and the anterior division of the transverse 
process of the fourth vertebra behind, with its dorsal surface in contact with the floor 
of the membranous sac (saccus paravertebralis) in which certain of the Weberian 
ossicles are contained (figs. 17 and 18, mph.r.). The connecting lobe stretches 
transversely across the ventral surfaces of the body of the first vertebra and the 
adjacent portion of the basioccipital. The anterior surface of the gland is convex, 
and is closely invested by a strong transversely disposed aponeurotic membrane. 
The peritoneum (fig. 23, p.) invests only the ventral surface of the air-bladder, 
extending laterally on to the side walls of the abdominal cavity, but in the medio- 
ventral line forms an incomplete mesentery, and is subsequently reflected on to the 
dorsal surface of the stomach ; anteriorly, it is continued forwards from the ventral 
surface of the bladder over the corresponding surface of the “ head kidney,” and, after 
blending with what we shall subsequently refer to as the “ aponeurotic membrane,” 
is reflected backwards on to the dorsal surface of the oesophagus. Near the antero- 
lateral regions of the air-bladder the peritoneum by a characteristic reduplication 
forms on each side a deep csecal pouch, with a somewhat restricted communication 
with the general peritoneal cavity, which extends outwards towards the inner surface 
of the proximal half of the clavicle and tlie root of its posterior process. These 
peritoneal cul-de-sacs exist in all Slluroid Fishes, and invariably contain prolongations 
of the lateral lobes of the liver. Their formation appears to be due to the unusual 
lateral extension of the anterior third of the air-bladder and the abutment of its outer 
walls against the inner surfaces of the lateral cutaneous areas, the partial displacement 
of the lateral hepatic lol)es from their normal position between the air-bladder and 
the side walls of the body, which this modification involves, being compensated for by 
the outward and forward protrusion of a portion of each lobe into special peritoneal 
pouches. The position and relations of these pouches as well as the recesses for the 
“head kidney” are shewn in Auchenoglanis hiscutatus (fig. 44,^?.c.s., and mph.r.). 
Internally to its peritoneal coat the air-bladder is partially invested by a membrane 
which is obvious enough where it is in relation with what, for the present, we may 
call the proper anterior wall of the bladder, but in most instances is extremely 
difficult to trace elsewhere. In the former position it exists as a thin, but fairly 
* Otherwise the anterior lymphoid expansion formed by the fusion of the nght and left halves of the 
mesonephros. 
