338 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
Depression of the defensive ray is, of course, produced by its own 
depressor ; but it is permitted by the action of the erector of the 
second, which draws its ray upwards, setting it astride of its spinal 
process, and releasing its limbs from their apposition with the fourth 
spinous process, and so allowing of its depression. It is to be noticed 
that the erection of the third and succeeding rays is accompanied or 
succeeded by the contraction of the depressor of the second and 
similarly their depression with the action of the second erector. 
The abnormal relations of these muscles can be explained by the 
modifications of the parts. Those of the anterior ray, which is 
almost unrecognizable and firmly fixed, are aborted. The interspinal 
of the first ray having lost its original relations and become bent 
upwards from its attachment to the spinous process of the third 
vertebra until it lies longitudinally, its muscles have lost their attach- 
ment to it, and so the erector of the second which ought to arise from 
its posterior surface has transferred its attachment to the more solid 
horizontal plate. The second depressor ought to arise from the 
anterior surface of the second interspinal, but the membrane bone 
which develops round the fourth vertebra, growing in as it were 
between the muscle and the interspinal, separates them, and the 
muscle passes farther forwards on the plate until it reaches the base 
of the anterior ascending process, thereby acquiring greater obliquity 
of action. The erectors and depressors of the third ray have in part 
their normal relations, but owing to the weight and ossification of 
the ray they have to move, have become enlarged, and extended their 
origin beyond the typical limits. The erector of the fourth ray has 
been crowded out from its original insertion by the aggression of the 
third depressor, and has become inserted into the horizontal plate 
where its action is more forcible. 
X.—MUSCLES OF THE ANAL FIN. 
The infracarinales act to a certain extent upon the rays of the 
anal fin. The portion named by Owen the ‘ retractor ischii,’ is 
inserted posteriorly into the base of the anterior ray, the posterior 
portion is inserted into the base of the posterior ray. Thus, when 
these act simultaneously, or even when one acts and the other remains 
fixed, the rays will be divaricated. 
