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THE MYOLOGY OF AMIURUS CATUS. 347 
less retrogression of the branchial apparatus, there has been, parr 
passu, an extension forwards of the hyopectoralis. The hyoid 
apparatus virtually covers in the branchial arches, and the muscle 
losing its attachment to the fifth branchial arch has extended for- 
wards and become attached to extremity of the hyoid, thus retaining, 
of course, its original innervation. 
The pharyngo-claviculares give a certain support to this idea. The 
phar.-clav. int. appears to be composed of the most external fibres of 
the ventral musculature of the first or first and second spinal seg- 
ments. The innervation in Amiwrus would assign it to the first seg- 
ment only, but Vetter has described its innervation as being from 
the first and second spinal nerves. In this case, then, we have a 
muscle whose fibres run in the same direction as those of the hyopec- 
toralis, whose origin is the same, and whose innervation is the same, 
and which retains the insertion which one would assign to such a 
muscle on theoretical grounds, and therefore indicates that a change 
such as has been described above has taken place in the hyopectoralis. 
The pharyngo-clavicularis eat. comes from fibres slightly external 
to the irternus. Its innervation in Amiwrus refers it to the first 
spinal segment. Vetter, however, states its innervation to be from 
the vagus. Theoretically one would certainly expect the innerva- 
tion described for Amzwrus, or even that described for the phar.-clav. 
int. by Vetter. I am inclined to believe that the innervation given 
by Vetter for the eaternus is a mistake, since in all its relations the 
muscle belongs to the spinal segments. 
The musculature of the trunk is divisible into a dorsal portion, 
which is not however constrictor, and a ventral, of which the hyopec- 
toralis is the anterior portion and the hyobranchialis the anterior con 
tinuation. The segmentation of the dorsal portion is very complete, 
and the innervation of the segments by their proper spinal nerves is 
throughout typical. The organs of locomotion have in certain places 
brought about certain departures from the general regularity. The 
fins, paired and unpaired, will be spoken of later. Just now atten- 
tion is directed to the swpra- and infracarinales. Concerning these 
the points to be noted are the almost complete absence of any signs 
of segmentation on the surface, while below it is very evident ; and, 
secondly, the innervation. In both cases the innervation is practi- 
cally a plexus. In the infracarinales, branches from the ventral 
stems of certain spinal nerves unite to form a plexus by which the 
muscle is supplied, and in the supracarinales the R. lat. trigem. acts 
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