ON THE ANATOMY OF FISHES. 
129 
A very characteristic feature in Arius piclada, and in all the Arioid genera and 
species that came under our notice, is the existence of a stout conical subvertebral 
process of bone which grows downwards from the ventral surfaces of the anterior 
portion of the complex centrum, the body of the first vertebra, and the hinder part of 
the basioccipital (figs, 45 to 48, sv.p.). All three bones apparently take part in its 
formation, but the basioccipital to a much greater extent than the others. The 
process is broad at its origin, somewhat laterally compressed for the greater part of 
its extent, but flattened from before backwards at its free ventral extremity. Its 
base is perforated by the commencement of the aortic canal. The subvertebral 
process is closely applied to the mesial portion of the anterior wall of the air-bladder, 
but, except at its distal extremity, there is no fibrous connection between the two 
(fig, 48, sv.p.). The formation of the process seems to have been due to the enormous 
enlargement of the accessory articular processes of the basioccipital and the centra of 
the first and complex vertebrae (see Macrones, p. 76, figs. 4 and 5), but if this be so 
their original paired arrangement is now completely obscured by ventral coalescence 
beneath the dorsal aorta. There can, however, be little doubt that the superficial 
ossifications by their extension into the median portion of the transverse membrane, 
and possibly also into that part of the aponeurotic membrane which invests the 
ventral surface of the basioccipital, combined with their subsequent fusion with the 
processes in question, have largely contributed to the growth of the subvertebral 
process. A somewhat intermediate condition between the ordinary accessory articular 
processes of Macrones and the subvertebral process of Arius and its allies is to be 
found in Auchenoglanis and one or two other genera, where the articular processes 
retain their usual paired arrangement, but those belonging to the complex centrum, 
and to a lesser extent those of the first vertebra also, obviously owe their lateral 
growth to an extension of bony deposit from the superficial ossifications into the outer 
layer of the tunica externa of the anterior waU of the air-bladder. 
As in Platystoma, the superficial ossifications are very strongly developed (figs. 45 
and 47, so.s.). Not only do they continuously invest the lateral surfaces of the 
anterior vertebrae from the complex to the seventh, inclusive, but, by their extension 
downwards and subsequent fusion in the medio-ventral line, they convert what is 
ordinarily a groove for the dorsal aorta into a complete aortic canal (figs. 46 and 47, 
a.c.). Laterally, the ossifications extend outwards from the sides of the centra and 
extensively invest the ventral surfaces of the transverse processes of the fourth and 
fifth vertebrae, and, in addition, slightly overlap the roots of the corresponding 
processes of the sixth and seventh vertebrae (fig. 47, so.s.). Anteriorly, the ossifica- 
tions extends downwards towards the median line, and would seem to blend with the 
posterior face of the subvertebral process. At the posterior aperture of the aortic 
canal the confluent ossifications are deeply emarginate in the mid-ventral line, fl'he 
shape of each ossification as it extends outwards from the vertebral centra to 
blend with the transverse processes is somewhat triangular, with the apex directed 
MDCCCXCIII. — B. s 
