THE MYOLOGY OF AMIURUS CATUS. 34& 



porting maxilla, the muscle has extended farther forwards than in 

 any other Teleosts hitherto described. The muscles are very mobile 

 structures, modification being in them more frequent and more com- 

 plete than in the nerves, ifcc. 



The add. hyomand., add. operc. and lev. operc, are all very closely 

 related, not only in position but also in innervation. They belonged 

 originally to the same constrictor layer from which the add. arc. pah 

 developed, constituting the posterior part of it. The lev. operc. is a 

 specialization of the superficial fibres of the most posterior portion — 

 that portion from which'also the add. operc. originated. These three 

 muscles and the add. arc. pal. are comparable to the dorsal portion 

 of the constrictor of the Elasmobranchs ; the geniohyoid 'eus, hyohyoi- 

 deus and portion of the intermand. being comparable to its ventral 

 portion. 



The Branchial Muscles. — The muscles supplied by the glossophary- 

 ngeal and vagus are small in bulk when compared with those already 

 discussed. In the Teleosts the muscles chiefly concerned in the re- 

 spiratory act are not those belonging strictly to the branchial but 

 those of the mandibular and hyoid arches. It is by means of these 

 that the cavity of the mouth is increased, and thus an inflow of water 

 produced, and it is by them also that the water is forced out below 

 the opercular apparatus, passing in its way over the branchial fila- 

 ments. Accordingly, we find the branchial muscles somewhat retro- 

 graded in bulk from the condition seen in the Elasmobranchs, and 

 this retrogression has been accompanied by a corresponding increase 

 in size and strength of the hyoidean and mandibular muscles. 



I regret exceedingly that I cannot give details in regard to the 

 innervation of many of the muscles, but, nevertheless, there are 

 certain points which may be indicated. Most of the muscles of the 

 branchial arches may also be reduced to the constrictor type, however 

 much they may be modified. In the first place the lev. branch, are 

 evidently the superior portions of the constrictor musculature, as are 

 also the mm. trans, dors, and interarc. obi. dors. The latter have 

 been slightly diverted from their constrictor direction, but as their 

 name implies are still somewhat oblique. The lateral portion of the 

 original constrictor has entirely aborted in Amiurus, though in certain 

 forms, as Esox, muscles are found at the angles of the arches, i.e., 

 where the upper limbs join the lower. No such muscles could,, 

 however, be detected in Amiurus. 



