398 ON THE STRUCTURE OF THE MOUTH 
The convex lower surface of the labrum bounds the mouth in 
front, while behind, it is limited by a transverse thickening of the 
chitinous integument, which appears to represent the sternum of the 
mandibular somite (fig. 40). The mouth opens into a very curious 
pharynx, formed by a delicate outer investment, and a strong inner 
chitinous lining. Viewed laterally, this organ (c) has the shape of a 
pear, its broad end being uppermost, and its long axis directed 
obliquely upwards, and backwards, in such a manner, that the broad 
upper end lies in the middle, between the prongs of the fork-like 
apodeme, which M. Blanchard has described. Viewed from above or 
below, however, the pharynx appears to be very narrow, indeed, 
almost linear, in consequence of its very peculiar form, which is dis- 
played in the section, taken transversely to the longitudinal axis and 
perpendicularly to the vertical plane represented in fig. 5. The cavity 
of the sac is here seen to be triradiate, while its walls are very closely 
approximated, so as to leave but a slight interspace. The narrow 
band which joins the two lateral walls below and behind is slightly 
excavated, so as to present a convexity towards the cavity of the 
pharynx. The two shorter rays of the sac are turned upwards and 
outwards; the third longer ray is directed vertically downwards. 
The cesophagus, an exceedingly delicate and narrow tube, comes off 
from the posterior wall of the vertical ray or crus of the pharynx, 
just above the mouth ; and, widening, passes backwards and upwards, 
into the dilatation which receives the ducts of the so-called salivary 
glands (e). Just above the aperture is a rounded projection (fig. 6 9), 
which I suspect may act as a sort of valve, when the sides of the 
pharynx are divaricated, by more or less completely occluding the 
cesophageal aperture. The inner surface of the chitinous lining of the 
pharynx is more or less rugose : and, towards the cesophageal aperture, 
presents a number of very minute spines (fig. 6). 
The transverse muscular fibres (fig. 2 2), rightly said by M. 
Blanchard to arise from the forks of the apodeme (7), are inserted 
into the side walls of the pharyngeal sac, which is so narrow from side 
to side, as readily to escape notice, without dissection. The termina- 
tion of the aorta appeared to me to pass between the two superior 
crura of the sac. 
The large vertical muscles (fig. I g) are, as M. Blanchard states, 
inserted into the base of the apodeme; and, besides these, the 
labrum is traversed by strong transverse and longitudinal muscles. 
The mode of action of this curious apparatus appears to be 
readily intelligible. Scorpions, as is well known, suck the juices of 
their prey, and the pharyngeal sac seems to be well calculated to 
