332 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
of other fishes. Owen describes them in Perca as forming a pair, 
in two layers, on both the outer and inner sides of the antibrachio- 
carpal base: and the fibres of one layer run obliquely ina different 
direction from those of the other layer in both pairs of muscles. 
The outer pair abducts or protracts the fin, the inner pair adducts or 
retracts it, sweeping it back into contact with the flank: the first 
movement might be called ‘extension,’ the second, ‘ flexion.’ The 
muscles in Amiurus can be reduced to a similar plan. 
2. ABDUCTOR SUPERFICIALIS (No. 14, Cuv.; Superficial abductor, Ow.) 
Consists of two portions, both lying in the groove on the under 
surface of the horizontal (inner) portion of the clavicle, and covered 
by the ventral musculature of the trunk. They pass over the bridge 
formed by the process of the coracoid, which articulates with the 
anterior ridge of the clavicle, and are inserted into the inferior’ sur- 
faces of the bases of the rays. The anterior portion (Fig. 5, AbS') 
is the smaller, and is partly concealed by the posterior. It arises 
from the outer portion of the anterior ridge of the clavicle, and is 
inserted into the inferior process of the base of the first ray. The 
posterior portion (AbS’) arises from the posterior ridge and floor of 
the groove, and is inserted by as many tendons into the bases of the 
rays, except the first. 
Innervation.—Supplied by a nerve arising from a branch which is 
composed of fibres from the external branch of first spinal, and from 
a branch from the united second and third spinal. 
Action.—Abduct the fin. When the deep abductors are acting, 
they will also separate the rays. 
3. AppucTor pRoFUNDUS (No. 15, Cuv.; Deep abductor, Ow.) 
This is also divided into two portions, both of which, however, 
are inserted into the base of the first ray. The first (Figs. 5 and 6, 
AbP’) lies below (i.e. dorsal to) the abductor sup., and arises from 
the posterior surface of the anterior ridge of the clavicle and from 
the floor of the groove. It passes below the bridge formed by the 
coracoid, and is inserted with the second portion into the base of the 
semi-circular process of the first ray. The second portion (Figs. 5 
and 6, AbP*) arises from the upper (dorsal) surface of the coracoid 
1The terms ‘inferior’ and ‘superior,’ etc., are applied to the parts as they are when the 
fin is abducted, i. ¢., extended at right angles to the body. 
