ParkER AND Rich—Ox the Myology of Patlinurus Edwardsi, Hutton. 161 
The deep extensors are much larger than the superficial, and lhe immediately 
beneath them. They consist of paired longitudinal bands extending continuously 
from end to end of the abdomen and connected by delicate aponeurotic bands with 
the anterior border of each tergum.* At the places of origin of the aponeuroses 
the muscle is constricted so as to have a distinctly segmented character. Like the 
superficial, the deep extensor of each side is divisible into a mesial and a lateral portion: 
in the mesial portion the fibres take a spiral course, in the lateral portion they are 
straight. 
The deep extensors are continued into the thorax to a far greater extent than 
the superficial. The muscle of each side arises by five distinct slips from the portions 
of the epimeral plate corresponding to the five legs. The slips, uniting, form a strong 
band which passes backwards, inwards, and slightly upwards to the terguin of the 
first abdominal segment, to which it is connected by a sheet of ligament. The 
portion of the deep extensor contained in the sixth segment, and acting as a levator 
of the telson, presents only one obliquely placed bundle of fibres on each side of the 
middle line. 
The ventral muscles (figs. 2, 8, 9 and 10) of the abdomen also consist of a 
superficial and a deep layer, the former of which are pure flexors, while the latter act 
partly as flexors, partly as extensors. 
The superficial flexors consist of extremely delicate sheets of muscle in close 
contact with the sternal integument, and passing from the posterior edge of a given 
sternum to the posterior edge of the sternum next following. Each imter-sterna! 
space contains two such muscular bands set somewhat obliquely a short distance from 
the middle line so as to enclose a V-shaped space with its apex backwards. 
The superficial flexor of the first abdominal segment arises from a process of the 
sternal region of the thorax between the origins of the fourth and fifth pairs of legs. 
The deep ventral muscles are of immense size and extraordinary complexity. They 
differ in important respects from those of Homarus, as described by Milne-Edwards ; 
unfortunately we have no spirit specimens of the latter genus for comparison. 
On viewing the whole of the ventral muscles from above as they are exposed by 
the removal of the terga and of the dorsal muscles, there is seen in each of the first 
five segments of the abdomen, as well as in the posterior region of the thorax, a 
paired transverse band of muscle, the fibres of which turn downwards both mesially 
and laterally so as to form a loop or arch open below. These bands may be 
* The extensors are incorrectly figured by Huxley (‘‘ The Crayfish”), Howes (‘‘Atlas”), and Lang (** Text-book of 
Comp. Anat.”’) as being inserted into the inner surface of the tergum near the middle. 
WwW 
