ON THE ANATO^ilY OP FISHES. 
231 
more or less well-marked oblique lateral ridges, which coincide witli the mesial attach- 
ment of the do7’sal edge of the transverse membrane, and not infrequently, also, with 
the corresponding attachment of the anterior pillars of the air-bladder. An osseous 
nodule (radial nodule) is invariably attached to the dorsal and hinder extremity of 
each lateral ridge, sometimes by anchylosis, especially in old specimens, but more 
frequently by a firm fibrous union. These nodules coincide with the fixed attachment 
of the radial fibres of the tripodes. A slender lamina or spicule of bone is prolonged 
from the dorsal extremity of each lateral ridge, from which, however, it is often 
distinct, and passing obliquely backwards and outwards ventrad to the cardinal 
groove, extends for a varying distance on to the ventral surface of the transverse 
process of the fourth vertebra, and finally blends therewith. Tliis lamina (dorsal 
lamina) corresponds with the dorsal attachment of the transverse membrane, and 
posteriorly often receives the insertion of a sheet of fibres derived from the lateral 
portions of the primary transverse septum of the air-bladder. 
The lateral surfaces of the complex and fifth centra are almost always traversed 
by deep grooves which are situated between the dorsal margins of the superficial 
ossifications and the roots of the modified transverse processes. As a rule each 
groove is completely encircled by bone only in the region of the dorsal lamina, but in 
those cases {e.g., Arius, Osteogeniosus) where the superficial ossifications extend from 
the sides of the complex and fifth centra on to the ventral surfaces of the transverse 
processes of the fourth vertebra, the groove becomes a complete canal for its whole 
length. The grooves transmit tlie posterior cardinal veins, and very generally also 
the attenuated anterior portions of the mesonephros as they pass forwards to join the 
so-called “ head kidney ” anteriorly. In correspondence with the unsymmetrical 
development of these veins, the right cardinal groove or canal is always much larger 
than the left. 
Stout subvertebral processes are frequently developed in relation with the anterior 
end of the complex centrum. In some forms [Arius and its allies) the process is a 
strong conical structure apparently formed by the downward growth and coalescence 
of processes derived from the ventral surfaces of the basioccipital and the first and 
complex vertebrae, but thickened posteriorly by the superficial ossifications of the 
complex centrum. In others {e.g., Plotosus) paired processes, formed apparently Ijy 
an extension of bony deposit from the superficial ossifications of the complex centrum 
into the mesial portion of the transverse membrane, may together form a transversely- 
disposed, fan-shaped subvertebral process. In Plotosus the latter only are present, 
but in Auchenoglanis an additional pair of similar but smaller processes are developed 
from the ventral surface of the body of the first vertebra, and serve to buttress 
anteriorly the former pair. All such subvertebral processes, while partially owing 
their formation to an exaggerated development of the accessory articular processes 
which are normally present in some Siluroids {c.g., Macrones), are, nevertheless, 
greatly thickened and enlarged by their association with the contiguous superficial 
