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PROFESSORS T. W. BRIDGE AND A. C. HADDON 
exhibits but a slight modification of the transverse arrangementj in the dorsal wall, on 
the contrary, the fibres become more or less oblique, and in the ventral wall oblique 
or even longitudinal. On the other hand, the fibres of the outer stratum, although 
somewhat iiTegular in their course, are mainly longitudinal in the ventral wall, but 
oblique in the dorsal and anterior walls, and curvilinear in the lateral. It is the 
specialization of particular tracts of fibres for the attachment of the walls of the air- 
bladder to fixed or moveable skeletal elements that is mainly responsible for the many 
marked deviations from the normal arrangement. 
Broadly speaking, it may be concluded that in Macrones the air-bladder consists of 
two physiologically distinct portions, a posterior, including the two lateral compart- 
ments, which from its septate or camerated structure can have but little capacity for 
change of volume in the way of distension, and an anterior chamber which is obviously 
capable of such volumetric variations. And also that any variations in the capacity 
of the anterior chamber can only be produced by lateral bulging or contraction in 
which the anterior, posterior, dorsal, and ventral walls have no share. It may further 
be concluded that as the fibres of the lateral and antero-lateral walls of the chamber 
are directly inserted into the tripodes at one extremity while remaining actually or 
relatively fixed at the other, any lateral variations of its internal capacity must impart 
corresponding movements to the tripodes and to the remaining Weberian ossicles. 
As regards the histological structure of the air-bladder we have nothing to add to 
Macullum’s description of Amiurus (24), which agrees substantially with that 
previously given by Leydig (22) for other Siluridse. We can also confirm in the case 
of Macrones Macullum’s statement as to the absence of muscular fibres in the walls 
of the bladder of Amiurus. 
In many Teleostei specially developed retia mirabilia or “ vaso-ganglia,” invested by 
a special modification of the epitheliiun of the tunica interna, are present, usually in 
the form of conspicuous flesh-coloured projections into the cavity of the air-bladder. 
Neither in Macrones nor in any other Siluroid that we examined were these structures 
present; and we are able to confirm Macullum’s statement {loc. cit.) that the epithelium 
presents no special or local modifications where it invests the capillary plexuses. 
The Relations of the Spinal Nerves to the Anterior Vertehrce and the Weberian 
Ossieles. — The mode of exit of the anterior spinal nerves from the neural canal, as 
well as their peripheral distribution, are substantially the same as described by 
IIamsay Weight in the case of Amiurus catus (42), but on one interesting point with 
reference to the relations of the roots of the third spinal nerve to the intercalarium, 
which has an important bearing on the exact homology of that ossicle, Macrones 
differs from Amiurus. Owing to the absence of an ascending process in the inter- 
calarium and the generally reduced condition of that ossicle in the latter Siluroid, 
Bamsay Weight was unable to satisfy himself as to its exact relations to the nerve 
in question, and consequently missed an important item of confirmatory evidence in 
support of the view originally suggested by Baudelot, and subsequently adopted by 
