[ 397 i 
the hdes of the fifh at the anterior end, where it inclofes 
more of the lateral parts of the body, becomes narrower 
towards the end of the tail, occupying lefs and lefs of 
the lides of the animal, till at laft it ends almoft in a 
point. Thefe two organs are feparated from one 
another at the upper part, by the mufcles of the back, 
which keep their pofterior or upper edges at a conlidera- 
blediftance from one another below that, and towards 
the middle, they are feparated by the air-bag ro; and 
at their lower parts they are feparated by the middle 
partition They begin forwards, by a pretty regu- 
lar edge, almoft at right angles with the longitudinal 
axis of the body, lituated on the lower and lateral parts 
of the abdomen. Their upper edge is a pretty ftraight 
line, with fmall indentations made by the nerves and 
blood veflels, which pafs round it to the ikin. At the 
anterior end they go as far towards the back as the mid- 
dle line of the animal ; but in their approach towards 
the tail they gradually leave that line, coming nearer 
to the lower furface of the animal. The general fhape 
of the organ, on an external or lide view, is broad at the 
end next to the head of the animal, becoming gradually 
narrower towards the tail, and ending there almoft in a 
point. The other furfaces of the organ are fitted to^ 
the ftiape of the parts with which they come in contadt;, 
therefore on the upper and inner furface it is hollowed,, 
to receive the mufcles of the backr^.’. There is alfo a lon- 
gitudinal depreflion on its lower edge, where a fubftance: 
{h) PI. IV. cccc. (c) PI. IV. ». (d) PI. IV. K. {e) PI. IV. 
Ues„ 
