il8 DR. L. A. BORRADAILE ON THE 
is fringed on both edges with long hairs, and the ventral (hinder) surface of 
the flange of the coxa upon which it stands is very hairy. The flagellum of 
the exopodite bears a fringe of long, feathered hairs, many of them jointed. 
A more detailed description of the hair-system of this and other limbs of the 
Shore Crab is given by Mcintosh (11). With its functions I will deal later. 
The cuticle of the third maxilliped, except the flagellum and the bkide of 
the epipodite, is hai'd and pigmented, like that of the rest of the exposed 
surfaces of the body. In this respect it contrasts strongly with that of the 
other mouth-parts. 
The muscular system, of the third maxilliped closely resembles that 
described by Pearson (13) for the same limb of the Edible Orab, and I have 
not examined it further than was necessary tQ assure me of this fact. Each 
of the joints of the limb has a flexor and an extensor muscle, those of the 
coxa and basi-ischium arising from the endophragmal skeleton and being 
inserted by conspicuous tendons, those of the remaining joints arising each 
from the joint preceding that ujjon which it is inserted. The exopodite has 
flexor and extensor muscles for the stem, which they enter from the coxa; 
but the flagellum has an extensor only, and must be brought back into the 
flexed position by its elasticity. The epipodite possesses muscles, but its 
most important movements are probably those which it carries out passively, 
under the action of the powerful muscles of the coxa. 
The action of the flexors and extensors of the coxa is to draw the whole 
limb to and from the normal position, in which its median edge meets that 
of its fellow on the middle line. In moving outward it passes a little 
ventrally, so that it clears the sub-branchial region of the carapace. This 
movement at the same time uncovers both the mouth-field and the inhalent 
opening of the gill-chamber, and sweeps the epipodite under the gills, as 
I will explain later. The movements of the basi-ischium are more 
complex. They may be analysed into : (a) a movement to and from the 
middle line independently of the movement of the coxa, (6) a dorso-ventral 
rotation, like the letting down of a flap, (c) a rotation about a longitudinal 
axis on the outer side of the limb, like the opening of a door, (d) a divarica- 
tion of endopodite from exopodite. This latter movement must be due to a 
contraction of the extensor muscle of the exopodite sinmltaneously with that 
of the flexors of the basi-ischium, for this bears the exopodite and tends to 
carry it in its own direction. The other movements of this joint are more 
difficult to understand, since they seem to take place with a good deal of 
independence, and the muscular apparatus does not appear to be adequate 
for this. Actually, they are performed together, combined into a single 
sweeping movement whose direction is decided by the form of the articula- 
tion between basi-ischium and coxa, but a compensating movement of the coxse 
can keep the edges of the t\\o limbs together, so that they are let down as a 
flap without at the same time necessarily opening as a pair of doors, though 
