174 Macreay Memoriat Vouume. 
The zzxfervor levator is a large cylindrical muscle arising from the outer surface 
of the external coxal plate and inserted, without a tendon, into that portion of the 
proximal border of the basipodite which is bounded above by the tendon of the 
superior levator and below by the infero-lateral hinge. The portion of the basipodite 
to which this muscle is attached is thickened and serrated for its insertion. 
The depressor is a large two-headed muscle. The outer head arises from the 
inner surface of the external coxal plate, the inner head from the internal coxal plate: 
the two heads unite in a large calcified tendon which is inserted into the mesio-ventral 
corner of the proximal edge of the basipodite. 
The zschzopodrte, or third podomere of the antenna, has three muscles, two levators 
and a depressor, all arising from the basipodite. The surface of origin of the depressor 
is increased by the inflection of part of the ventral region of the proximal border of 
the basipodite in the form of a small upstanding plate situated immediately laterad 
of the insertion of the depressor tendon described in the preceding paragraph. 
8. Extrinsic muscles of the antennule (figs. 21-23). 
fo) 
The articulation of the antennule is quite different from anything we have met 
with or seen described in the Arthropoda, This appendage is attached to the ventral 
end of the zxter-antennulary bar, a strong vertical plate connecting the prostomial 
plate (v7de zexfra) with the pseudepistoma. The basal podomere of the antennule is 
connected with its articular cavity by a very wide arthrodial membrane which 
extends all round the joint, there being no peg-and-socket articulations visible 
externally. Movement is possible in all planes, but, contrary to what would be 
expected from the extent of the arthrodial membrane, the antennule cannot be pulled 
in and out but always remains at a constant distance from its articular cavity. 
The explanation of this peculiarity is as follows :—The mesial border of the 
articular cavity is produced into a strong calcified peg which passes downwards, 
outwards and forwards, so as to project into the base of the antennule. A similar 
peg arises from the dorsal surface of the first segment of the antennule, near its 
proximal edge, and passes backwards and downwards, its apex coming in contact 
with that of the previously mentioned peg and articulating with it. In this way an 
internal articulation is produced, allowing of universal movement. 
The muscles of the antennule present very striking peculiarities. The appendage 
is raised by a long evator which arises from the infra-ophthalmic bar of the 
prostomial plate (vzde zufra, p. 175), and is inserted by a calcified tendon into the 
arthrodial membrane on its dorsal side. There is a small adductor arising from the 
inwardly projecting lateral edge of the inter-antennulary bar, and an adductor arising 
from the middle region of the bar; both are inserted into the arthrodial membrane. 
