50 



BULLETIN OF THE BUREAU OF FISHERIES. 



ABDUCTOR PECTORALIS PROFUNDUS. 



When the superficialis muscle fibers are reflected the abductor profundus is exposed. 

 It arises from the ventral surface of the coracoid. Beginning at a point one-third the 

 distance from the anterior end there is a thick muscular mass intimately attached into 

 the surface of a triangular area on the ventral face of the coracoid. The base of this 

 triangle is marked by a line parallel with the base of the pectoral fin over the union of 

 the coracoid with the basalia. The profundus has a short, heavy tendon divided into 

 slips corresponding with, and inserted into, the inner margins and tips of the curved 

 bases of the ventral half rays of the pectoral fin under the tendons of the superficialis. 



The contractions of this muscle draw the fin downward, helping to balance or 

 support the body when quietly resting on the bottom. 



EXTENSOR PECTORALIS. 



There is a rather thick muscular bundle which arises under the anterior origin of 

 the abductor superficialis and along the margin of the ventral portion of the clavicle. 



Fig. 7. — Ventral view of the pectoral fin muscles. A segment is cut out of the anterior end of the protractor ischii, pr. i.. together 

 with the anterior ventral portion of the lateral muscle. This uncovers the abductor superficiaHs. ab. 5., and its attachments 

 to the ventral half-rays of the fin. The end of the extensor, £x. , with its insertion into the base of the first fin ray is shown. 



This muscle lies close within the angle formed in the ventral surface of the clavicle. It 

 is inserted by a short thick tendon into the external surface of the base of the first fin ray. 



Contraction of this muscle spreads the fin out in the horizontal position. When 

 the fin is folded back against the body the external ray forms the upper margin of the 

 fin. From this position the extensor pectoralis throws the fin forward, bends it slightly 

 downward and spreads the rays. The muscle tends to support the abductor. 



The great lateral muscles are attached by strong slips into the clavicle just dorsal 

 to the insertion of the pectoral fin. There is also a muscular slip from the great lateral 

 muscle running just ventral to the base of the fin and inserted into the fascia of the 

 dorsal wall of the pericardium. This fascia is closely attached to the internal or ventral 

 margin of the coracoid. Undoubtedly contractions of the great lateral muscle would 

 tend to draw the pectoral girdle posteriorly. When the fascia is dissected off a rather 



