192 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
membrane, either through an inv^asion of ossified deposit extending from originally more 
normal transverse processes, or, as in the case of the ventral processes, by the ossifica- 
tion of the ventral portion of the membrane in continuity with the superficial 
ossifications of the complex centrum. 
The bilobed anterior division of the mesonephros occupies a recess of corresponding 
shape, immediately in front of the two funnels, to the anterior wall of which, and to 
their investing membrane the gland is closely applied. 
The peritoneum covers the ventral surface of the mesonephros, and, anteriorly, is 
continued over the under surfaces of the funnels. Although elsewhere easily separable 
from the latter, the peritoneum is firmly adherent to the fibrous portion of their walls, 
along the horizontal median line of their ventral surfaces, or, more correctly, along the 
interspace between the recurved margins of the transverse processes of the fourth and 
fifth vertebrae. This attachment seems exactly to correspond to a similar connection 
between the ventral edge of the transverse membrane and the peritoneum in Macrones. 
Anteriorly to this point the peritoneum invests the ventral surface of the bilobed 
portion of the mesonephros, and from thence is reflected on to the posterior 
face of the septum separating the abdominal and branchial cavities, ultimately 
becoming prolonged backwards on to the dorsal wall of the oesophagus, A little in 
front of the outer extremity of each funnel the peritoneum grows out through 
the ventro-lateral muscles, and terminates in a relatively spacious cul-de-sac, between 
the funnel and the axilla of the pectoral fin, and immediately beneath the external 
skin. Each peritoneal sac contains a small diverticulum from the adjacent lateral lobe 
of the liver, which is connected by a slender stalk with the abdominal portion of the 
gland. In a somewhat similar fashion a lateral prolongation from the anterior portion 
of the mesonephros also bulges outwards through the ventro-lateral muscles, and 
occupies a recess situated just behind the mouth of the funnel and close to the super- 
ficial skin, but, unlike the hepatic outgrowths, has no peritoneal investment. 
In addition to the fibrous investment which covers the osseous funnels and closes 
their distal apertures, the latter are also in close relation with lateral areas of the 
external skin. The lateral-line canal, with two of its tubular ossicles, and the lateral 
branch of the tenth cranial nerve, cross each area as they pass backwards from the 
skull. 
As far as the shape and general relations of the air-bladder are concerned, Taylor’s 
description (loc. cit.) is perfectly accurate. The organ consists of two thin-walled 
pyriform sacs, which occupy and completely fill the cavities of the two bony funnels 
(fig. 80, a.s.). Each sac is connected with its fellow by a narrow tubular portion 
which crosses the median line, ventrad to the centrum of the complex vertebra, and 
also to the aortic groove and dorsal aorta, and, in so doing, traverses deep eniargina- 
tions in the aortic ridges.* The walls of each air-sac are everywhere in close contact 
* In a specimen twelve and a half inches long, the length of each sac when measured from the middle 
of the tubular portion was 15 mm., and the maximum width 6 mm. 
