THE SPIDERS OF EPPING FOREST.
185
Sternal Plates. These are two strong chitinous pieces placed
below the cephalo-thorax, one between the coxal joints
of the palpi, the other between the coxae of the legs.
The former is known as the Labium, the latter as the
Sternum. The Labium is a small plate, usually of a
somewhat oblong or semi-oval shape, sometimes plane,
at other times having its anterior edge turned outwards
or thickened along its external surface, this form being
known as recurved. The Sternum is a rather large plate,
usually more or less oval or cordiform, which occupies
the central portion of the inferior surface of the cephalo-
thorax. To this structure the true legs are attached.
In a few cases projecting portions of the sternum pass
beyond the attachments of the coxae, thus forming a
kind of socket for the reception of each leg.
Falces. The falces are a pair of appendages situated beneath
the anterior extremity of the cephalo-thorax. Each falx
consists of a stout basal joint surmounted by a movable
fang, this latter being pierced by a channel whose open-
ing is near the point of the fang. Connected with each
channel is a poison gland, sometimes placed within the
basal joint, sometimes within the cephalo-thorax and
sometimes partly in each. Upon the external surface
of the basal joint is often found a smooth raised portion
or basal protuberance, and in some species the falx is
externally striated. This structure is apparently
employed as a stridulating organ, being actuated in this
capacity by a process upon the inner surface of the
palpus. The fang, when at rest, lies in a depression at
the extremity of the basal joint, known as the fang-groove:
this latter is often provided, at one or both of its edges
with teeth or denticulations. The basal joint is sometimes
furnished towards its extremity with a dense tuft of
hairs, known as a scapula.
Palpi. The palpi are a pair of limbs which are attached to the
underside of the cephalo-thorax, one upon each side of
the labium. Each palpus consists primarily of five
distinct joints, Coxa, Trochanter, Femur, Tibia and Tarsus.
These parts are also known amongst various authors as
exinguinal, humeral, cubital, radial and digital joints