UN THE ANATOMY OE FISHES. 
85 
abruptly bent inwards upon itself, so that its posterior, or, more correctly, its inner 
extremity, which is slightly decurved, is in contact with the lateral surface of the 
complex centrum at a point behind and above the thickened dorsal extremity of the 
radial nodule (fig. 3). In shape the process greatly resembles a sickle, having its 
inner concave edge partially encircling the radial nodule, and its convex outer margin 
directed at first outwards, and then bent directly inwards. From the convex outer 
mai-gin, and at the point where the process first commences to curve inwards towards 
the complex centrum, a slender heel-like process is given off which is directed out- 
wards and a little forwards towards the antero-lateral angle of the air-bladder (figs. 
12 to 14, tr.h. ; also figs. 3, 18, and 19). Although not in actual contact, the 
crescentic process, the root of the transverse process of the fourth vertebra, is 
intimately related to its dorsal surface. The articular process of the tripus is a 
somewhat triangular outgrowth from the inner margin of the ossicle at the junction 
of its anterior and crescentic processes (figs. 12 to 14, tr.cu\). The process is 
flattened in a horizontal plane, and its upper and lower surfaces coincide in direction 
with those of the remainder of the ossicle. Near the anterior margin of its dorsal 
surface there is a thin vertical ridge, which slopes upwards towards the distal or 
inner extremity of the process, and then becomes a vertical elongated condyle (fig. 13, 
dr.). The condyle articulates with the lateral surface of the anterior third of the 
complex centrum, that is, the centrum of the third vertebra, at the bottom of the deep 
pit-like depression, situated immediately in front of) and dorsad to, the radial nodule. 
A vertical ridge also traverses the ventral surface of the crescentic process, com- 
mencing at the root of the heel-like j)i'Ocess, and from thence extending obliquely 
forwards and inwards on to the ventral surface of the articular process (figs. 12 and 
14, v.r.) The ridge lies much nearer to the inner than the outer margin of the 
crescentic process, and for a part of its course follows the curvature of the former. 
Only a slight interval separates the anterior end of the ridge from the thickened 
dorsal portion of the radial nodule, the two being exactly opposite each other (figs. 
3 and 20). We shall call this ridge the ventral ridge of the tripus. 
The tripus is freely moveable in a lateral plane on its articulation with the complex 
centrum by means of the articular process, and it is evident that its anterior and 
crescentic processes represent the two arms of a lever, the fulcrum of which is the 
vertebral connection of the articular process. 
We append the following measurements of the Weberian ossicles of a specimen of 
Macrones nemurus eight inches in length, but it may be remarked that the dimensions 
of the ossicles are liable to considerable variation according to the size of the particular 
example examined : — 
