332 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



of other fishes. Owen describes them in Perca as forming & pair, 

 in two layers, on both the outer and inner sides of the antibrachio- 

 carpal base : and the fibres of one layer run obliquely in a 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.; Super jicicd 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 1 sur- 

 faces of the bases of the rays. The anterior portion (Fig. 5, AbS 1 ) 

 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 2 ) 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. Abductor 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 1 ) 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 4 ) arises from the upper (dorsal) surface of the coracoid 



iThe terms 'inferior' and ' superior,' etc., are applied to the paTts as they are when the 

 fin is abducted, i. e., extended at right angles to the body. 



