~ aa 
THE MYOLOGY OF AMIURUS CATUS. 341 
muscle do not arise from the succeeding axial ray but may be traced 
across it and several others to the fascia near the axial line, so that, 
viewed as a whole, their arrangement resembles that of a fan. The 
central muscles above and below lie entirely on the axial surface of 
the ray to which they are attached, and, since there is no median 
impaired ray, their fibres arise from the fascia between them and 
partly also from the fascia of the superficial muscle. These intrinsic 
muscles approximate the rays, being aided by the upper and lower 
portions of the deep musculature and opposing the upper and lower 
portions of the superficial muscles. 
Innervation.—The intrinsic muscles are supplied from a plexus 
formed by ventral branches of spinal nerves xxxili.—xli. The 
muscles above the spinal cord are supplied by branches from F#. lat. 
trigem., and from the small posterior 2. dorsales spinales. 
On comparing the myological characters of the head of a Teleost 
with those of a Selachian, the first point that strikes one is the ab- 
sence in the former of the well-marked constrictors found superfici- 
ally in the latter ; in other words, the direction of the muscle fibres 
in the Teleosts appears to be more longitudinal than in the Selach- 
ians, and therefore the myomeres more similar to those of the trunk. 
1t has been shown by Balfour and Gette that the musculature of the 
head develops in exactly the same manner as that of the trunk, 7.e., 
from the primitive vertebre, and is, therefore, segmental in its ori- 
gin, a myomere lying between the arches of each pair of vertebrae of 
which the head is composed. In Amphioxus there is no differentia- 
tion of the myomeres, the musculature from the tail to the head con- 
sisting of a series of similar myomeres separated by similar myocom- 
mata’, and therefore represents more closely the original type than 
does the arrangement in either the Selachians or the Teleosts. Ac- 
cordingly, the Teleosts would at first seem to present a more primi- 
tive type than do the Selachians, but a closer investigation shows 
this to be a mistake. 
When one takes into consideration the presence of an osseous, and 
therefore more or less immovable, cranial skeleton in the Teleosts, 
the absence of the constrictors is easily understood. But even then 
one would suppose that in the more movable parts the constrictors 
1 The ventral musculature of Amphiorus would interfere with this generalization were it not 
that it must be considered as belonging to a different category from the trunk musculature. 
