NO. 1788. NORTH AMERICAN ERGASILID.^—WILSON^ 287 



SO but little flexion. The chief use of these muscles is to act as 

 shoulder flexors in moving the large second antennoe, and in accom- 

 plishing this they are assisted by four other muscles on either side. 

 One of these (c) is parallel with them and removed some distance 

 farther back. It extends from a point near the mid line diagonally 

 outward and strikes the lateral margin a little behind the three just 

 mentioned. 



The second (d) starts from this marginal end of the first and runs 

 forward and inward, nearly parallel with the carapace margin. The 

 third (e) and fourth (t) are curved and extend from the junction of the 

 first and second downward and inward to the base of the second 

 antennae. These seven muscles on either side thus form an armature 

 sufficiently powerful to manipulate the large second antennae. 



The diagonal muscle (c) is united at its posterior end with a pair 

 of broad and ribbon-like curved muscles (/), which occupy the center 

 of the head on either side of the mid line, and form a dorsal muscular 

 band (m. &.), which serves as a basis of support and attachment for 

 the muscles already described. Just outside this band there is a 

 single muscle (g) on either side, which is the longest in the body. It 

 reaches from the base of the second antennae back through the head 

 and first thorax segment, and into the second thorax segment, to 

 whose dorsal surface its enlarged posterior end is attached. This 

 powerful muscle aids in controlling the second antennae, and also 

 produces flexion between the head and thorax. Exterior to this long 

 muscle and parallel to it is a much shorter one Qi), extending from 

 the base of the second antennae back nearly to the center of the first 

 thorax segment. This muscle produces flexion of the head upon the 

 first thorax segment, and is assisted in this by a curved muscle (i), 

 which arises much farther back on the dorsal surface of the head and 

 runs through the first two thorax segments. This last muscle is 

 divided near the center of the first segment and attached to the dor- 

 sal surface of the latter. It thus produces flexion not merely between 

 the Jiead and first segment, but also between the first segment and 

 the three which follow it. 



The remaining dorsal muscles consist of three on either side of the 

 mid-line, which originate some little distance apart at about the mid- 

 dle of the head and beneath the transverse muscle band, and which 

 converge rapidly backwards. 



The outer one (j) is narrow in front and widens a little posteriorly, 

 reaching to the posterior border of the second thorax segment. The 

 middle one (k) is wider in front and narrows posteriorly, and also 

 stops at the posterior border of the second thorax segment. The 

 inner one (I) is the same diameter throughout, but only reaches a little 

 beyond the center of the first segment. These muscles all produce 

 flexion between the head, the first and the second thorax segments. 



