292 SIR JOHN LUBBOCK ON THYSANURA. 
4. This muscle is one of those that move the tail. It rises close to, but at the side of 
the preceding, and passes diagonally backwards and downwards, curling round no. 5, 
which will be described next, and eventually reaching its posterior attachment at the 
dorsal side of the root of the tail. 
5. This muscle rises with a double head immediately below the preceding, and, passing 
backwards, twists as it were round it, and is also attached to the posterior margin of the 
following segment. 
6, 7. Thisisa transverse muscle. Its upper end is double, and is attached not far from, 
but rather in front of, the middle of the segment. It passes straight down, and is inserted 
into the central ventral piece. 
8 is inserted close to the anterior end of no. 5, and passes diagonally backwards and 
downwards, outside no. 6, and is attached to the lower side of the penultimate segment. 
9 lies immediately outside no. 4, but is somewhat straighter, as it is not affected by 
Bo... «bs 
10 rises nearly in the centre of the side-wall, opposite the middle part of no. 6, and, 
passing backwards, is attached close to the posterior end of no. 4. 
11 lies just outside no. 10, and has the same direction and attachments. In some 
specimens these two muscles seemed to form one only. 
12. This powerful muscle is the principal extensor of the tail, and passes forwards 
along the ventral surface, through the antepenultimate segment, and is attached at the 
anterior end of the third abdominal segment. 
Third Abdominal Segment.—1. This muscle corresponds to the muscle, no. 1, of the 
fourth segment, immediately in front of which it lies, and with which, in some speci- 
mens, as already mentioned, it even forms one continuous muscle. It generally, how- 
ever, commences near the middle line of the back, on the side of the dorsal vessel, and 
directly in front of the anterior end of the corresponding muscle of the following seg- 
ment, and, passing straight forwards, is attached to the anterior margin of the segment. 
2. This muscle, as in the fourth segment, is smaller than, and lies under, or rather. 
outside of, the preceding. 
3 rises at the anterior end of the segment, partly under and partly at the side of 
no. 1, and passes rather diagonally backwards under no. 2. 
4 runs at the side of, and parallel to, no. 3. 
5 rises at the side of no. 1, and passes forward parallel to it, but, instead of being 
attached at the anterior end of the segment, passes forward, completely through it, to 
the anterior edge of the second, where it is inserted, partly below, and partly at the side 
of, the muscle no. 1 of that segment. 
6, 7. These two muscles correspond to those which I have indicated by the same 
numbers in the fourth abdominal segment. They rise, side by side, at the lateral edge 
of no. 5, and not very far from the anterior margin of the segment. They are largest at 
their dorsal extremity, and pass straight downwards. ; 
8. This powerful muscle rises at the anterior margin of the antepenultimate segment, 
at the side of no. 5, and passes downwards and forwards, dividing into two branches, 
which, at their lower and anterior extremity, are intimately connected with the neigh- 
