142 Cc. H. DANFORTH 
an oblique canal through the cartilage, (b) from its dorsal expan- 
sion above the canal, (c) from the inner side of the clavicle, and (d) 
from the dense tissue around the corocoid fossa medially. Fibers 
of this group mostly become tendinous toward their insertion. 
Finally, the deepest fibers arise from the basalia and radialia of 
the fin itself. As stated above these various fibers are not sepa- 
rated into groups and the areas over which they arise form one 
continuous field. The muscle bundles are inserted directly or 
by small tendons into the curved ventromedial ends of the bony 
rays of the dorsal moiety of the fin. 
Innervation. The chief supply is a large nerve which results 
from a plexus of the second, third and fourth spinal nerves. 
There is also a plexus formed from the’ fifth and sixth spinal 
nerves and twigs from this also reach the muscle by running 
along the ventral side of the basal cartilage. 
Blood supply. "The muscle is supplied by the ultimate branches 
of the subclavian in anastomosis with the coronary artery. 
Action. It adducts the fin drawing it up and toward the body. 
Adductor of the pectoral fin: figure 8, m.abp. 
This muscle arises (a) from a small area on the ventral side 
of the clavicle towards its anterior end, (b) from a membrane 
bridging the fontanelle between this part of the clavicle and the 
pectoral cartilage, (c) from a furrow on the lateral aspect of the 
cartilage, and (d) from the ventral side of the basale and radialia 
of the fin. It is inserted on the base of the ventral moiety of 
the dermal rays. The most dorsal fibers, arising from the over- 
shelving lateral expansion of the cartilage, are inserted on the 
anterior ray by a small separate tendon. 
Innervation. Nerves reach the muscle in three ways. The 
largest supply is a nerve derived from the above-mentioned plexus 
of the second, third and fourth spinal nerves which reaches the 
muscle by coming in back of the clavicle, across the adductor 
and through a large foramen in the cartilage. The second is a 
small branch of the same plexus which reaches the muscle by 
passing medial to the cartilage. The third is derived from a 
