FISHES, 297 



The Radys (No. 43) which sustain the branchiostegal membrane, 

 adhere by moveable articulation, often by simple ligaments, to the 

 lower border of the two principal pieces of each branch,* the anterior 

 are generally articulated to the border; the posterior are scare ly 

 more than attached to the external surface, near the border. Their 

 number and forms vary much; in the carp there are only three, and 

 in elops there are more than thirty ; the most common number 

 at least in the aeanthopterygians is seven, as in the perch. 



This os hyoides can be raised and depressed, and carries with it the 

 branchi, and even the lower jaw. When drawn by the widening of 

 the palato temporal lamina, it can also render the angle of its branches 

 more open, and thus enlarge, in concert with the operculum, the 

 opening of the gills. The radys attached to it, have also their particular 

 movements of widening and closing, and extend or fold the membrane 

 which they support. 



The Bones which support the Branchi.^ 



Fishes only breath by forcing out at the sides of their necks the 

 water which they take in at their mouths ; it thus passes between 

 the branchi, which are a sort of comb, in general four at each side, 

 formed of a great quantity of their narrow, forked, membranous or 

 cartilaginous laminae, placed in fishes after one another. These 

 four pairs of branchi, are supported by four pairs of arches, adhering 

 by their inferior extremities to the two sides of a chain of intermedi- 

 ate small bones, which chain is attached in front in the angle of the 

 os hyoides, between the four anterior pieces and above its tail. These 

 same arches become curved as they ascend, - and fix their other 

 extremity under the cranium, by cellular tissue, or ligamentous attach- 

 ments only. 



The intermediate chain of small bones forms a sort of continuation 

 to the lingual bone. In general there are threes of these small bones; 

 the first (No. 53)§ is attached in the bottom of the angle formed by 

 the branches of the os hyoides ; the second (No. 54 (a) is behind the 

 first, and affords attachment to the first pair of arches ; the third 

 (No. 55 (6) and last, gives attachment to the second pair ; the third 

 pair of arches adheres to its extremity, and the fourth is attached in 

 the angle of the third ; lastly the inferior pharyngians are attached in 

 the angle of the fourth. 



The arches are composed, each of two parts, which are moveable 

 on one another. The inferior is that which is attached to the inter- 

 mediate chain of small bones, and in the three first pairs, is formed 

 of two pieces, one internal shorter(c) (No. 57) the other external(d) 

 longer (No. 58) ; in the latter pair there is but one piece (No. 60). 



* These are the sternal ribs of Mr. Geoffroy. 



f There is a view from above of the bones of the branchi, and the pharyngeans 

 •with the os hyoides, and in their natural position represented in pi. III. fig. vi. ; 

 and those of one side with the two parts of their arches extended, pi. III. fig. vii. 



% M. Geoffrey regards them as articulations of the body of the hyoid. 



§ The Basi-hyal of M. Geoffroy. 



(a) The ento-hyal of M. Geoffroy. 



(b) The uro-hi/al of M. Geoffroy. 



(c) The thyreals and aritheals of M. Geoffroy. 

 (rf) The inferior pleurals. 



