Parker and Rico—Ox the Myology of Palinurus Edwardsit, Hutton. 167 
4. The external flexor is reinforced by a band from slip No. 6 of the thoracico- 
abdominal muscles. 
5th segment. 
1. There is an additional longitudinal flexor furnished by the inner limb of the 
enveloping muscle of the fourth segment. 
2. The accessory oblique extensor, the external accessory longitudinal flexor, and 
the external flexor are absent. 
6th segment. 
1. The superficial and accessory oblique extensors, and the accessory longitudinal, 
oblique, external, and superficial flexors are absent. 
The longitudinal flexor is furnished from the inner limb of the enveloping 
muscle of the fifth segment. 
7th segment (telson). 
The only axial muscles connected with the telson are a pair of deep extensors 
and a pair of flexors arising from the sternum of the fifth segment. 
The lateral muscles of the abdomen consist of a single muscle (fig. 4) on each 
side called by Howes the levator abdominis. In our opinion the action of this muscle 
is more accurately expressed by calling it a rotator. We have observed in the living 
animal that the abdomen can be rotated, as a whole, upon the cephalothorax, this 
movement being rendered possible that there are no articulations between the 
posterior end of the thorax and the first abdominal segment, the two being connected 
merely by the loose thoracico-abdominal membrane. 
The rotator abdominis is a large three-headed muscle. The larger head arises 
from the inner surface of the carapace just posterior to the cervical groove, and above 
the branchio-cardiac groove. The middle head arises from the dorsal edge of the 
epimeral plate in the region of the seventh thoracic segment. The short head arises 
from the epimeral plate just below and behind the preceding. The three heads unite 
into a single tendon, which is inserted into a small sclerite* connected with the 
anterior border of the first abdominal segment. 
Acting together these muscles must draw the abdomen forwards, at the same 
time raising it slightly : acting separ ately they obviously act as rotators, each raising 
* Marked a in Huxley’s “‘ Crayfish,” fig. 38, and representing la of what Howes (‘‘Atlas”) calls the ‘‘ Thoraco- 
abdominal linkwoik” in Astacus. 
