ANATOMY OF HETERODONTUS: ENDOSKELETON 473 
mal of which is long, the distal represented by a tiny cartilagi- 
nous tip. Anteriorly a much enlarged fused first radial strikes 
the basal plate almost at right angles. In the end of this, as 
well as in the end of the basal piece, is a fossa, by means of which 
articulation with the pelvic girdle is effected. From this first 
radial cartilage three rows of radialia project. In the first are 
one or two small cartilages; in the second, two or three; and in 
the third there are four cartilages similar to the segments in 
the first radialia of the basal piece. From the basipterygium 
thirteen rows of radialia are given off. These are terminated 
by smaller radial cartilages in the more anterior rows but in 
the three posterior rows each one consists of two segments. 
3. The skeleton of the pelvic fin of the male is, with slight 
modifications, like that of the female. It consists of the basi- 
pterygium and its radials. In the male there are fourteen radials 
which meet the basipterygium at an angle of forty-five degrees. 
The most anterior of the radials represents the fusion of three 
cartilages which, like those following, are segmented into two or 
three pieces. The most posterior radials, unlike those in the 
female, are unsegmented. The inner lobe of the pelvic fin in 
the male (fig. 27) is modified as a framework for the clener or 
copulatory organ. 
The basipterygium in the male is continued by the basal piece 
(ba.) to which it is connected by two short segments (b'”). At 
the angle between the basipterygium and the basal piece there 
arises from the former the so-called ‘beta’ (8) cartilage. The 
basal piece is generally round, but terminally it is flattened and 
possesses a groove which passes obliquely across to the dorsal 
side. Several cartilaginous pieces appear near the terminal part 
of the groove. These are two dorsal terminals (d.tr.1-2), a dorsal 
marginal (d.mg.), and one ventral terminal cartilage (v.tr.). 
Proximal to the ventral terminal there is an accessory termi- 
nal (tr.3). 
b. The skeleton of the unpaired fins. 1. First dorsal fin (fig. 24). 
Extending from the vertebral column one-half the length of the 
long anterior fin-spine, or to the point externally where the 
spine emerges from the skin, is a thin basal cartilage, the base of 
