252 Proceedings of the Royal Society of Edinburgh. [Sess. 
times seen. The crab is a very slow animal in its movements, and, if it 
has not succeeded in autotomising a damaged leg after about a minute, it 
begins slowly to pluck at it, just as the hermit crab does. 
The structure of the basal limb-segments in all the Brachyura is almost 
uniform. The second segment (basi-ischium) is divided by a furrow at 
the breaking-plane into two parts. It is connected by muscles to the 
first segment and to the body wall, the short extensor and the short fiexor 
moving it on the first segment, and the long extensor and long flexor 
V- 
Fig. 17. 
Figs. 16 and 17 show the arrangement of tendons and muscles at the limb-base in Carcinus mcenas. 
(Fig. 17 is after Fredericq. ) B.p., breaking-plane ; s.f., short flexor ; l.f., long flexor ; s.e., short 
extensor ; l.e., long extensor ; d., diaphragm. 
joining it to the body. The bellies of these last muscles pass through the 
cavity of the first segment. Figs. 16 and|17 show this arrangement from 
the lateral aspect, and looking through the limb-cavities, respectively. 
As the tendon attachments of the extensor muscles are of great im- 
portance in the later description of the process of autotomy. they must 
be described in some detail. 
Looking at the upper division of arthrodial membrane of the articulation 
between the second and third limb-segments, we see the tendons shining 
through in the region of their attachment to the lower edge of the basi- 
ischium. The long extensor is attached anteriorly and the short posteriorly. 
If a knife is passed between the tendon heads of the muscles it will be 
found that if the handle is turned towards the head region of the crab 
