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PROFESSORS T. W. BRIDGE AND A. C. HADDON 
cases the modified transverse processes are provided with powerful protractor muscles, 
in the form of specialized portions of the dorso-lateral musculature, which have their 
origin on the posterior face of tlie skull and their insertion into the anterior surfaces 
of the terminal oval plates. The transverse processes of the fifth vertebra are, as a 
rule, but moderately expanded, although in one case {e.g., Platystoma) they may be 
as greatly expanded as the preceding processes with which, in this genus, they are in 
sutural union anteriorly. They are often confluent at their roots with tlie transverse 
processes of the fourth vertebra, but their distal extremities are always free. Rarely 
are they rudimentary {Anchenipterus) or absent [Oxydoixis). Like their predecessors 
they have their origin from the neural arch instead of from the centrum, but always 
at a slightly lower level than the former. The transverse processes of the sixth 
vertebra vary greatly in size and in degree of expansion. They may be greatly 
expanded and suturally united to those of the fifth vertebra (Flatystoma), or, while of 
slightly greater length, may not be more expanded than the normal processes wlficli 
follow them. Their origin is always from the centrum of their vertebra. Usually 
they carry the first pair of ribs, but in at least two geiiera [Calhchroiis and Crypto- 
pterus) the latter are supported by the transverse processes of tire fifth vertebra. 
A continuous deposit of superficial bone invests the lateral surfaces of more or 
fewer of the anterior vertebral centra. It varies greatly in thickness as well as in 
extent in different Siluroids, and sometimes forms no inconsiderable portion of the 
otherwise somewhat attenuated anterior centra. The centra of the complex and fifth 
vertebra are invariably so invested ; less frequently the deposit may extend on to the 
lateral surfaces, or at all events along the ventro -lateral margins of the sixth and seventh, 
or even the eighth vertebrie. The ossifications are always strongly developed along 
the ventro-lateral edges of the centra they invest in the form of parallel ridges, which 
enclose between them a deep median groove for the dorsal aorta {e.g., Macrones). By 
the ventral union of these ridges the groove may become converted into a com- 
plete canal {Arius, Auchenipterus, Platystoma, Ac.). Exceptionally, the dorsal aorta 
appears to burrow its way through a canal in the centra of the complex, the fifth, 
and the sixth vertebrse {Platystoma), a fact which in this case is apparently due to 
the unusual thickness of the investing superficial ossifications. The ossifications may 
also extend laterally on to the ventral surfaces of more or fewer of the anterior 
transverse processes, forming a floor for the cardinal grooves, and thereby converting 
the latter into complete canals {e.g., Arius, BatrachocepAialus, O.steogeniosus, Ac.). 
They usually obscure the intervertebral sutures between the different vertebral 
centra, but sometimes {e.g., Platystoma) the sutures are obvious externally on the 
surface of the investing ossifications in the form of wavy interdigitatlng lines. 
Special developments of the system of superficial ossifications also take place in 
relation with the skeletal attachments of the air-bladder in the region of the complex 
veitebra. The anterior margins of the ossifications Investing the sides of the complex 
centrum are thickened near tlie anterior extremity of the latter in the form of two 
