ON THE ANATOMY OF FISHES. 
215 
The transverse process of the fourth vertebra is cleft to its root into distinct 
anterior and posterior divisions. The former {tp.'^a.), as in Auchenipterus and 
Malapterurus, has an oblique origin from the neural arch of the complex vertebra, 
and from thence curves slightly forwards, and at the same time downwards, in the 
form of a thin and highly elastic lamina of bone, and finally terminates by expanding 
into an oval plate, the long axis of which is directed from its dorsal extremity 
downwards, and a little outwards and forwards. The faces of the plate are somewhat 
oblique, but nevertheless look almost directly forwards and backwards respectively. 
The posterior face is nearly flat, but roughened by faint longitudinal ridges ; the 
anterior face, on the contrary, is thickened and somewhat convex, more especially 
near its dorsal edge, where it becomes continuous with the elastic root. The margins 
of each plate are thin and extremely brittle. The protractor muscle of the plate 
(figs. 91, 92, has an origin similar to that of the corresponding muscle in 
Auchenipterus, and an insertion which coincides with the thickened dorsal part of the 
anterior face of the plate. As in other Siluroids with an “ elastic-spring ” apparatus, 
the spring and its terminal plate are widely distinct from the post-temporal, and in 
no way contribute to the support of the pectoral girdle. The posterior division of the 
transverse process (fig. 90, tp^p.) is not decurved, but forms a horizontally arranged 
and somewhat expanded flat plate of bone. The transverse process of the flfth 
vertebra {t.p.^) is similar in shape, but more slender, and at its root slightly overlaps 
the preceding process. The transverse processes of the sixth vertebra (t.pA) are 
normal, and to their distal extremities the first pair of ribs (r.^) is attached. 
The superficial ossifications (fig. 90, s.os.) are thickest where they invest the lateral 
surfaces of the complex centrum, but gradually thin away posteriorly until they are 
reduced to comparatively inconspicuous ridges along the ventro-lateral margins of the 
fifth and sixth vertebral centra. Their ventral margins form two longitudinal ridges 
which enclose between them a well marked groove for the dorsal aorta. On each of 
the lateral surfaces of the complex centrum there is a short oblique ridge, and at the 
dorsal extremity of this a short radial nodule (r.n.). A dorsal lamina (d.l.) is prolonged 
from each nodule in the form of a thin obliquely disposed strip of bone, which has the 
normal relations to the cardinal groove (cd.g.), and finally blends with the ventral 
surface of the posterior division of the transverse process of the fourth vertebra. 
As in Auchenipterus and Synodontis, and, for the same reason, the inferior limb of 
the post-temporal (fig. 90, pt.i.) is strongly developed, and has an exceptionally 
extensive and firm articulation with the basioccipital : the ascending process also has 
an equally rigid connection with the skull. The posterior face of the inferior limb is 
slightly hollowed out for the reception of the oval plate of the “ elastic-spring ” 
mechanism when the latter is pulled forwards by the contraction of its protractor 
muscle. Normally a space of about 5 mm. intervenes between the two structures, and 
through this interval the oval plate moves according as it is pulled forwards by the 
