THE MYOLOGY OF AMIURUS CATUS. 333 
plate, and from the under surface of the portion of the clavicle over- 
lapping this. It passes below this overlapping portion of the clavicle, 
in the channel between it and the coracoid, and uniting with the 
first portion, is inserted with it. 
Innervation.—The same as for the abd. superf. 
Action.—This muscle abducts the first ray, and thus assists in 
abducting the entire fin, but at the same time it gives to the first 
ray the rotation which is necessary to complete its abduction and 
fixation. This rotation is brought about by the muscle being in- 
‘serted into the upper surface of the ray. 
The position of the second portion of this muscle appears some- 
what anomalous, inasmuch as it is apparently in the upper surface of 
the arch, the abd. superf., and even the other portion of the abd. 
prof., lying in its lower surface. An examination of the structure 
of the arch explains the anomaly. The posterior portion of the arch 
which unites with its fellow by suture is not the posterior portion of 
the clavicle as it has been usually described, but is an enlargement 
of the coracoid. Now this latter lies really on the inferior surface 
of the arch, and therefore the upper surface of this enlargement is 
applied to the under surface of the clavicle, and accordingly a muscle 
lying upon its upper surface may yet lie on the under surface of the 
clavicle. Though the two portions of the deep abductor are widely 
separated at their origins, yet their union before insertion indicates 
that they originally constituted one muscle, homologous with the 
deep abductor of Perca. 
4. ADDUCTOR SUPERFICIALIS. 
Arises from the inner surface of the ascending portion of the 
clavicle and from the bridge-like spiculum of bone near its base; the 
deeper fibres arising from the radialia. It is inserted into the 
superior surfaces of the bases of all the rays, except the first, dividing 
into a separate tendon for each ray. 
Innervation.—It is supplied by a branch from the combined second 
and third spinal nerves. 
Action.—Adducts the fin. When the fin is abducted the rhythmi- 
cal and successive action and relaxation of the superficial abductors 
and adductor will produce an undulatory movement of the fin. 
