THE MYOLOGY OF AMIURUS CATUS. 347 



less retrogression of the branchial apparatus, there has been, pari 

 passu, an extension forwards of the hyopectoralis. The hyoid 

 apparatus virtually covers in the bi-anchial 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 Amiurus 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, 

 an J 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 ext. comes from fibres slightly external 

 to the interims. Its innervation in Amiurus refers it to the first 

 spinal segment. Vetter, however, states its innervation to be from 

 the vagus. Theoretically one would cer-tainly expect the innerva- 

 tion described for Amiurus, or even that described for the phar.-clav. 

 int. by Vetter. I am inclined to believe that the innervation given 

 by Vetter for the externus 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 supra- 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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