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PROFESSORS T. W. BRIDGE AXD A. C. HADDON 
The first spinal or liypoglossal nerve perforates the exocclpital. Tlie second and 
third spinal nerves emerge from the neural canal between the claustruin anteriorly 
and the arch of the complex vertebra behind, but are invariably separated by the 
ascending process of the intercalarium whenever that process is developed, as in 
Macroncs, Liocassis, and Bagroides. The fourth and fifth spinal nerves traverse the 
neural arch of the complex vertebra, and the sixth the arch of the fifth vertebra. 
The additional spinal nerve described by Sagemehl in Silurus glanis as emerging 
between the claustruin and the ascending process of the scajjhium, we have never met 
with, although our attention has been specially directed to that point. 
The air-bladder varies greatly in degree of development, not only in different 
genera, but in different species of the same genus. Even individual variations are 
not infrequent, but it never exhibits that bipartite division into simple anterior and 
posterior sacs which is so characteristic of all other families of Ostariophysem. One 
of its most noteworthy features is a tendency to lateral development, whereby the 
outer walls of the anterior portion become applied, through the divergence of the 
dorso-lateral and ventro-lateral muscles of the body wall, directly to the external skin 
(“lateral cutaneous areas”). The insertion of the crescentic processes of the tripodes 
is always into the dorsal wall of the anterior chamber of the air-bladder in the normal 
Siluridte, or into the corresponding walls of the laterally situated air-sacs in the 
abnormal forms, and, as a ride, takes place in such a way that the fibres forming the 
anterior and lateral walls of each half of an anterior chamber, or of each air- sac, con- 
verge as they pass into and form the dorsal wall, and ultimately become inserted into 
the convex outer margin of the tripus of that side. Specialised fibres of the dorsal 
wall (“ radial fibres ”) converge like the radii of a circle from the inner concave margin 
of the crescentic process, and are inserted either directly into the adjacent lateral 
surface of the complex centrum or indirectly through the intervention of an osseous 
nodule (“ radial nodule ”). 
In nearly all Siluroids the lateral growth of the air-bladder, and the intimate 
relation of its outer walls to the lateral cutaneous areas, have led to the displacement of 
the lateral lobes of the liver and their enclosure within peritoneal cul-de-sacs, a con- 
dition which sometimes persists even in cases where the air-bladder has undergone 
partial atrophy. 
In no Siluridoe are special capillary tufts or retia mlrabilia (the so-called vaso- 
ganglia), invested by a special modification of the epithelium of the tunica interna, 
ever developed in connection with the air-bladder. 
As a convenient means of summarising the more important generic and specific 
variations, the Siluroids may be somewhat arbitrarily divided into two principal 
groups : — (1) the Siluridce normales, and (2) the Sduridiv, abnormales. In the former 
group the air-bladder is always well developed and subdivided internally into three 
intercommunicating compartments, of which one is anterior, and two posterior and 
lateral in position. The anterior and dorsal walls of the anterior chaml)ei‘ may be 
