176 Macrieay Memoria Vouvume. 
The eye-muscles are inserted partly into the inter-ophthalmic sclerite, partly 
into the basal sclerite, and partly into the eye-stalk itself. 
The depressor of the inter-ophthalmic sclerite is a large bipinnate muscle arising 
from the median coxal ligament, and passing upwards in front of the superior coxal 
muscle to a double insertion in the inter-ophthalmie sclerite. This muscle depresses 
the eye-stalks and at the same time rotates them slightly backwards. 
The levator of the basal sclerite arises from the inter-ophthalmic sclerite and 
passes across the dorsal region of the arthrodial membrane to be inserted into the 
basal sclerite. 
The rotator of the basal sclerite arises from the infra-ophthalmie bar of the 
prostomial plate in common with the depressor of the eye-stalk : it is inserted into 
the posterior edge of the basal sclerite and produces a backward rotation of the 
I g 
eye-stalk. 
The eye-stalk contains four small straight muscles which surround the optic nerve 
and ganglion and are all inserted into the distal region immediately proximad of the 
cornea. Of these one is dorsal, arises from the basal podomere and acts as a levator: 
the other three arise from the prostomial plate, the anterior one being an adductor, 
the posterior an adductor, and the ventral a depressor of the eye-stalk. 
SumMary. 
1. The great ventral mass of muscle in the abdomen, usually considered to act 
exclusively as a flexor, gives rise to slips which, being inserted into the terga of the 
segments above the hinges, and pulling in an almost horizontal direction, must act as 
extensors. 
2. The ventral (so-called flexor) muscles of the abdomen exhibit far greater 
complexity than would be gathered from Milne-Edwards’ description of the muscles 
of Homarus. We have found it necessary to make numerous additions to the 
terminology, as it was hardly possible to describe the various flexor and extensor 
slips without giving them appropriate names. A list of the slips inserted into a 
typical abdominal segment is given on p. 163. (See also diagrams, Pl. xx1.) 
3. The muscle usually called levator abdominis is more accurately called a 
rotator, since it is the chief agent in rotating the abdomen as a whole upon the 
cephalothorax. 
