THE MYOLOGY OF AMIURUS CATUS. So} 
a 
posterior belongs essentially to the branchiostegal rays. This por- 
tion (Fig. 3, Hh') arises from the inner surfaces of the operculum 
and interoperculum, extending from them to the dorsal border of the 
first branchiostegal ray Thence it passes below that ray to the dor- 
sal border of the second, and so on to the most internal ray, becom- 
ing narrower as it nears the median line, and having its central fibres 
better developed than the lateral ones. From the last ray the 
muscle extends upwards and forwards, and is inserted into the apon- 
eurosis which separates it from its fellow. 
The anterior portion (Fig. 3, Hh’), arises from the upper border 
and surface of the ceratohyal and hypohyal, and passing inwards is 
inserted into the aponeurosis between it and its fellow. 
Innervation.—R. hyordeo-mandibularis facialis. 
Action.—Both portions act as constrictors. The posterior portion 
will close the aperture of the gill cavity by shutting down upon it 
the branchiostegal membrane. The coimplete closure of the “ gill- 
slit” is necessary in order that the hyoid apparatus and its muscles 
may properly perform their pumping action. The anterior portion 
approximates the hyoid arches, and thus aids the posterior portion, 
drawing the whole hyoid apparatus towards the side of the skull. 
The hyohyoideus varies somewhat in different forms. In sox it 
passes as a continuous sheet over the branchiostegal rays, not passing 
from one to the other as in dmiwrus and the Cyprinoids. In Perca 
and Hsox the muscle passes directly across to the hyoid arch of the 
opposite side, and in the latter there isa separation into two bundles 
of which the outermost passes forward and is inserted into the cera- 
tohyal and hypohyal, and therefore corresponds to the anterior 
muscle of Amiurus. In Perca neither Stannius nor Cuvier nor Owen 
describes an anterior portion, but Owen states’ that “ In some fishes 
a transverse muscle, repeating the characters of 21, Fig. 135, (7. e., 
the intermandibularis), passes from one ceratohyal to the other.” Vet- 
ter terms that portion of the muscle which runs between the branchi- 
ostegal rays the ‘hyohyoideus superior, grouping those portions 
coming from the most internal ray and from the ceratohyal together 
as the ‘hyohyoideus wmferior,’ an arrangement which in “sox is 
quite proper, but will not hold with Amiurus. 
-1Qwen. — Loe. eit. 
