322 FISHES. 



of four on each side, and proceed from the azygos chain of small 

 bones to the inferior portion of each arch. The effect of their action 

 is to depress this part. 



The transverse superiors (No. 39) are three, and are sent off from 

 each pharyngean to the adjacent part of the arch. The latter is 

 common to the pharyngeans, and to the arches of both sides. 



There is only one inferior (No. 40) which is thick, and is between 

 one pharyngean and the other. 



The latter two muscles are employed in bringing together the 

 pharyngeans, and in contracting slightly the apparatus in a trans- 

 verse direction. The same effect is produced by the first, up to a 

 certain extent. 



This description of the muscles of the branchiae, which is chiefly 

 derived from the perch, applies to a large number of acanthoptery- 

 gians ; it does not however extend to all fishes, except with such 

 modifications as are of importance for the number and direction of 

 the ribbands belonging to the various fasciculi — modifications which 

 depend, as is very obvious, on the general form of the head, and on 

 the difference in size of the pharyngeans, as also on the functions in 

 which they employ the various sorts of contrivances wherewith they 

 are armed. We shall see some examples of this in the course of the 

 present work. 



But the differences which are more essential in their nature are 

 those observed in the chondropterygians. Their branchial apparatus 

 has no operculum, and is surrounded with a general muscular en- 

 velop, that is frequently reinforced by a, sort of ribs. We shall give 

 a description of them in detail, when we come to this grand division 

 of the class of fishes. 



So far as regards the analogies of these muscles, all that can be 

 said is that the fasciculus of suspensors has some relation with the 

 stylo-hyoideans and stylo-pharyngeans of man, and that the trans- 

 verse superiors can be compared to the hyo and to the crico-pharyn- 

 geans ; but these are affinities so very remote as that they cannot be 

 allowed to establish an undoubted analogy. 



CHAPTER V. 



Bruins and Nerves of Fishes, 



After having described the mechanism of their motions, we now 

 pass to the system of the nervous organs of fishes, or to that contriv- 

 ance by which this mechanism is put into action. 



This system is composed r as is the case with the superior tribes of 

 animals, of external senses, of a central medullary apparatus, and of 

 nerves which establish their communication. As, again, in the 

 higher orders, the central medullary apparatus, that is to say the 

 brain and spinal marrow, occupy the cavity of the skull and of 

 the vertebral canal. 



