ANATOMICAL NOMENCLATURE. 125 
In measuring the eyes, the unit for determining the distance between 
any two, as MF or MR, is the diameter of the pair under considera- 
tion. In measuring the distance between the middle group of eyes, 
whether of the front or rear row, and the side group, the unit of measure 
is usually the linear space occupied by the same, that is, the distance from 
outer margin to outer margin; in other words, the width of the front or 
rear sides of the middle quadrilateral. This line is spoken of technically 
as the “area” or the “alignment.” (Fig. 87, ar.) Thus the area of MF 
is the line from the outside of one midfront eye to the outside of the other. 
Sometimes the space between the midfront eyes is also used as a unit. 
The clypeus (cly, Fig. 87) is that part of the face lying between the 
front row of eyes and the anterior lower margin thereof, where it meets 
the mandibles. The clypeus is spoken of as “high” or “low,” as 
i ea the space above named is greater or less; or sometimes the words 
rab “wide” and “narrow” are used as equivalent to the above. The 
height or width of the 
clypeus is measured by the dis- 
tance of its margin from the two 
midfront eyes, and the diameter of 
one of these is the unit for such 
measurement, 
The views of the epigynum or 
external part of the female genital, 
in the various plates, are taken with 
the spider lying upon the back and ee 
the observer looking down upon her CEPHALOTHORAX AND PARTS THEREOF, 
from the direction of the spinner. "et. Cr, comet; om, const grooves th median 
ets. The drawings therefore show cap, caput; mg, margin of corselet; ¢.su, cephalic 
the lower side of the organ unless Str eh sve see: 0, orunrguad. Tio, Str 
otherwise specified. cones; ba, base of sternum; ap, apex of same; lab, 
The following terms are used in ?'™™5 ™ Maxille. 
describing the cephalothorax;: The dorsal part is known as the “ corselet”’ 
(Fig. 91, ers), of which the posterior part is the base (ba), and this is 
usually smooth, truncated, and indented where overhung by the 
abdomen. The depression on the summit is the median fosse, or 
simply “fosse” (fs); the slight furrows extending from the fosse 
to the insertion of the legs are “corselet grooves” (c.g) or furrows. The 
line of union between caput and corselet is the “cephalic suture” (¢.su) ; 
that part of the head extending from the suture to the vertex I have called 
the caput (cap), as distinguished from the vertex or forehead and the face. 
The under part of the cephalothorax is the sternum (Fig. 92, str), which is 
a more or less oval or cordate or subtriangular shield, sometimes much 
indented or scalloped at the coxal insertions and pointed at the base (ba). 
Opposite the coxse, in some species, are slight eminences technically referred 
Cephalo- 
thorax. 
