■[ 398 ] 
lies, which divides it from the fmall organ, and which 
gives a kind of fixed point for the lateral mufcles of the 
Its moft internal furface is a plane adapted to 
the partition which divides the two organs from one 
another The edge next to the mufcles of the 
hack is very thin, but the organ becomes thicker and 
thicker towards its middle, where it approaches the cen- 
ter of the animal. It becomes thinner again, towards 
the lower furface or belly ; but that edge is not fo thin 
as the other Its union with the parts to which 
it is attached is in general by a loofe, but pretty flrong, 
cellular membrane; except at the partition, to which 
it is joined fo clofe as to be almofl infeparable. 
The fmall organ lies along the lower edge of the ani- 
mal, nearly to the fame extent as the other r-v. Its fitua- 
tion is marked externally by the mufcles which move 
the fin under which it lies. Its anterior end begins 
nearly in the fame line with the large organ, and juft 
where the fin begins. It terminates almoft infenfibly 
near the end of the tail, where the large organ alfo ter- 
minates. It is of a triangular figure, adapting itfelf 
to the part in which it lies (^). Its anterior end is the nar- 
row^eft part; towards the tail it becomes broader; in the 
middle of the organ it is thickeft; and from thence be- 
comes gradually thinner to the tail, where it is very thin. 
The two fmall organs are feparated from one another 
by the middle mufcles, and by the bones upon which 
(f) PI. IV. (g) PI. IV. {h) PI. IV. (9 PI. n. fig. I. ILL. , 
(k) PL IV. II. 
the 
