320 ARACHNIDA—ARANEAE CHAP. 
and can generally be folded back upon the paturon, which often 
presents a groove for its reception. The Theraphosid spiders are 
distinguished from all others by the fact that the plane of action 
of the chelicerae is vertical and longitudinal. The paturon pro- 
jects forward in a line parallel with the axis of the body, and its 
distal end can be raised or depressed, but not moved laterally ; 
while the unguis in action has the point directed downwards, 
and, at rest, is applied to the under surface of the paturon. 
In other spiders the patura hang more or less vertically, 
and while to some extent mobile in all directions, their principal 
motion is Jateral, and the ungues have their points directed to- 
wards each other in action, and are applied to the inner surfaces 
of the patura in repose. The plane of action in this case is also 
more or less vertical, but transverse. 
The paturon is always extremely hard and strong. In Thera- 
phosae of burrowing habits the distal end is furnished with a 
group of powerful teeth, the “rastellus.” The 
groove for the reception of the unguis is often 
guarded on one side or on both by rows of teeth, 
the arrangement of which is frequently an im- 
portant specific character. The inner anterior 
border is also often furnished with a group of 
stiff hairs or bristles. This powerful joint is 
of use in crushing and expressing the fluids of 
‘ insects pierced by the ungues. 
Fie. 177, — Front The crescent-shaped unguis is tapering and 
view of Teaxtrix 5 
denticulata. x Smooth, except for the presence, on the posterior 
ee = ae surface, of one or two feebly dentated ridges. 
3, paturon, and Near its free extremity there is a small orifice 
ena ofcheli- Jeading to the poison reservoir and gland. 
In the genus Pholcus (see p.401) the chelicerae 
may almost be regarded as chelate, the unguis being met by a 
spiny projection from the inner anterior border of the paturon. 
Rostrum.—On examining a spider, even under a dissecting 
microscope, it will not be easy at first to discover the mouth. 
Indeed, Lyonnet had almost come to the conclusion that Spiders, 
like some Myrmelionid larvae, imbibed the juices of their prey 
by way of the mandibles, before he found the orifice and gave 
a remarkably accurate description of the adjacent parts. 
If a specimen be placed on its back, and the labium raised 
