304 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
anteriorly, is similar in appearance, but stouter. Distally, like the 
basale, it supports the fin rays, but proximally it articulates with the 
upper surface of the anterior extremity of the spicule-like bridge. 
Between the distal ends of this, which is a radial and the basale, is 
a small cartilage, embraced by the fin-rays. The next element, 
anteriorly, is a large cartilaginous nodule, articulating with the 
extremity of the rod-like process of the coracoid, and supporting the 
fin rays. It probably represents another radial. Huxley’s meso- 
pterygial basale is here, as is usual, ossified with the anterior fin ray. 
Concerning the majority of these structures nothing need be said 
but that they are on the same plan as the rays of the unpaired fins. 
The most anterior ray (fig. 7), however, requires special mention. It 
is completely ossified, terminates in a sharp point, and has the 
posterior edge*serrated. By special arrangements it can be firmly 
fixed in the erect position, and can only be depressed by rotation 
through an angle of 40°; it is therefore an important weapon for 
defence or offence. These arrangements are as follows :—From the 
upper surface of the base (the original mesopterygial basale) a high 
semi-circular ridge (s7) arises, and the proximal extremity terminates 
in two processes (tps and tpt), including a deep groove between them. 
When the fin is erected the semi-circular ridge runs into the semi- 
circular groove (fig. 7 sg) at the base of the inferior process of the 
mesoclavicula, and at the same time the outer edge of the coracoid is 
received into the groove between the two terminal processes. Move- 
ment directly forward or directly backward is now effectually 
prevented, and flexion can only be accomplished by rotation, when 
the ridge slips out of its groove, and the outer edge of the coracoid out 
of its groove. 
