ON THE ANATOMY OF FISHES. 
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to that of the fifth vertebra, which in turn may be similarly connected with the arch 
of the sixth vertebra, or the rigid union of the different neural arches may be effected 
by a firm sutural union only. Even when not actually anchylosed it is rare for the 
arches of the fifth, sixth, or seventh vertebrae to be movably articulated by means of 
pre- or post-zygapophyses as is the case with the normal free vertebrre that follow. 
The spinous processes of the third and fourth vertebrae are either confluent to form 
a thin vertical lamina of bone [Macrones), or fused only at their roots, their distal 
extremities being free and divergent {Arius). The spine of the third vertebra is 
almost always grooved anteriorly and inclined forwards over the body of the first 
vertebra to an articulation with the exoccipitals and supraoccipital ; in the groove a 
modicum of intercalated cartilage is very generally present, more especially in young 
or immature specimens. The spine of the fourth vertebra is usually directed back- 
wards and, like the succeeding spines, is generally cleft for the support of certain of 
the interspinous bones of the dorsal fin, but in the absence of the latter may, like its 
fellows, be simple and undivided {e.g., Malapteruriis). The spines which immediately 
succeed the foregoing may be rudimentary or obsolete [Arius), or well-developed and 
bifid ; not infrequently they are either partially anchylosed or firmly articulated 
to one another and to their predecessors. 
The transverse processes of the fourth vertebra, very frequently those of the fifth, 
and more rarely those belonging to the sixth vertebra [Flatystoma), are more or less 
expanded and by their partial anchylosis or sutural union form on each side of the 
vertebral column a broad wing-like plate of bone, the anterior margin of which is 
strongly decurved, for the investment of the anterior and dorsal walls of the anterior 
chamber of the air-bladder. The transverse process of the fourth vertebra has a 
broad flat root, and for the rest of its extent may be simple, or, as is more usually 
the case, cleft more or less deeply into distinct anterior and posterior divisions, of 
which the former is always strongly decurved towards its distal extremity and closely 
applied, even if not attached, to the lateral portion of the anterior wall of the air- 
bladder. The anterior division is usually applied distally to the inferior limb and 
stem of the post-temporal, and firmly united thereto by a ligament in such a way as 
to afford a rigid support to the proximal portion of the pectoral girdle. The entire 
transverse process invariably has its origin, not from the centrum, but from the whole 
length of the continuous neural arch of the complex vertebra. In certain Siluroids 
this process becomes modified to form the singular “ elastic-spring ” apparatus first 
described by Johannes Muller. In some of these forms [Malagterurus, Symdontis, 
Pangasius) each anterior division is almost completely separated from the posterior 
division, with an oblique origin from the arch of the comj)lex vertebra, and becoming 
flexible and liighly elastic, expands distally into an ovoid plate which is closely 
applied to the corresponding lateral portion of the anterior wall of the air-bladder. 
In others (e.y., Oxydoras and Auclienipteriis) tlie anterior division undergoes a similar 
modification, but tlie posterior division has become completely suppressed- In all such 
