[ 399 ,] 
the bones of the fins are articulated (», The large and 
the fmall organ on each fide, are feparated from one ano- 
ther by a membrane, the inner edge of which is attached 
to the middle partition, and its outer edge is loft on the 
llvin of the animaK'^A To expofe the large organ to 
view, nothing more is necelTary than to remove the Ikin, 
which adheres to it by a loofe cellular membrane. But 
to expofe the fmall organ, it is necefiary to remove the 
long row of imall mufcles which move the fin 
OF THE STRUCTURE OF THESE ORGANS. 
The ftrucfture is extremely fimple and regular, confift- 
ing of two parts; viz. flat partitions ov/epta, and crofs di- 
vifions between them. The outer edge of Xht^Q/epta ap- 
pear externally in parallel lines nearly in the direcflion of 
the longitudinal axK of the body (”). T\i^{efepta are thin 
membranes, placed nearly parallel to one another. Their 
lengths are nearly in the diredtion of the long axis, and 
their breadth is nearly the femi-diameter of the body of 
the animal ('>K They are of different lengths, fome being 
as long as the whole organ. I fhall defcribe them as 
beginning principally at the anterior end of the organ, 
although a few begin along the upper edge; and the 
whole, pafling towards the tail, gradually terminate on 
the lower furtace of the organ; the lowermoft at their 
origin terminating fooneft. Their breadths differ in dif- 
ferent parts of the organ. They are in general broadeft ' 
near the anterior end, anfwering to the thickeft part of 
(l) PI. m. E. (m) PI, IIP (n) P)-. II; KKK. (o) PI. UP hhI 
VoL, LXV. Hhh the 
