, g o M i c r o s c o p i c a l Essays.
Thefe four lines, which we may conceive to divide the caterpillar
longitudinally into four equal parts, are attended with this
remarkable eircumftance, that each o f them mark the place under
the Ikin that is occupied by a confiderable vifcera; the heart, or
rather the thread of hearts, lies under the fuperior line; the
fpinal marrow immediately over the inferior line; the two tracheal
arteries follow the courfe o f the lateral lines.
At equal diftances from the fuperior hnd two lateral lines, and
the inferior lines, we may fuppofe four intermediate lines. T h e
two between the fuperior and lateral lines are called intermediate
fuperior lines ; the two others which are oppofite to them, and
between the lateral and inferior lines, the intermediate inferior
lines.
A n E xplanation of Figures i and 2, Plate X I I ; or an
A ccount of the Muscles of the Caterpillar .when
opened b y the Bel ly .
O f all the interior parts o f the caterpillar, none prefent fo
beautiful a view, or a more wonderful and fymmetrical arrangement,
than that o f the mufcles; the more fo, if they are taken
away by equal ftrata on both fides, fo as to expofe at the fame
time the fimilar mufcles on the oppofite fide, and by this means
exhibit to the aftoniffied eye their ex aft form and eorrefpond-
ence.
Fig. 1 and 2 is a reprefentation o f the mufcles o f two different
caterpillars, opened at the belly, and fuppofed to be joined together
at the fuperior lines j for as the mufcles on the oppofite
6 fide
M i c r o s c o p i c a l E s s a y s . 331
fide of each caterpillar are perfeftly fimilar, it was not only un-
neceffary to reprefent them, but by joining another view of the
mufcles, as in Fig. 2, we are enabled to exhibit thofe mufcles
which were covered in Fig. 1, and by this means fave much time
in the defcription, and the addition o f another plate.
The dorfal mufcles, or thofe o f the back, are marked by capital
letters; the gaftric mufcles, or thofe o f the belly, by Roman letters
; the lateral mufcles by Greek charafters. Mr. Lyonet has
only given a name to thofe among the latter, which are marked
0; thefe are placed upon all the divifions, from the fecond to the
'eleventh ; they are called dividing mufcles, on account o f their
fituation; a mufcle that has been once marked with a letter
always retains the fame, both in the defcription and the other
figures.
P r e p a r a t i o n .
The caterpillar was emptied, and the mufcles freed from the
tnaffes o f fat, the nerves, and other veffels, which, if they had
■ been left, would have confufed the view o f the mufcles, and rendered
it difficult to diftinguiffi and trace them.
F i r s t R i n g .
The mufcle A is double. The anterior one is thick at top,
and feems to be divided into different mufcles on the upper fide,
but it has no fuch appearance on the under fide. One o f their in-
fertions is towards the head, at the fkin o f the neck ; the other
infertion o f the firft mufcle A is a little above, and that o f the
S s 2 fecond