INTERNAL ANATOMY. 339 
forward along it, sending off numerous branches to it and to the anterior end 
of the foot. This nerve may probably be considered to be the anterior pedal 
nerve proper, if such a one can be distinguished from the others sending branches 
to this region. 
The fifth, or median pedal nerve, 5, arises as a strong trunk from the ventro- 
lateral face of the pedal ganglion just behind the origin of the fourth nerve. It 
passes straight outward and downward, bifurcating into an anterior and a 
posterior ramus at the junction of the body-wall and the foot. These two 
divisions break up into numerous branches to the median and posterior regions 
of the foot. 
Close behind the origin of the fifth nerve is given off a nerve of nearly the 
same size, the sixth pedal nerve, 6, which likewise passes outward and backward. 
At about 10 mm. from its origin it divides into two nearly equal branches. 
The more anterior one of these curves outward and forward to the body-wall, 
forking as it reaches it. The anterior branch thus formed enters the wall slightly 
above the margin of the foot, and but slightly posterior to the level of the central 
neryous system. It then curves forward and dorsally, and ramifies among 
the deep muscles of the wall. Its fellow, the posterior branch of the anterior 
ramus, passes backward along the inner surface of the body-wall to which it 
gives off small branches, finally splitting up among the deep muscles. 
The posterior main ramus of the sixth nerve courses backward, bifurcating 
in front of the origin of the lower group of lateral retractors of the head, the 
branches immediately entering the wall of the body and ramifying to the deeper 
dorso-lateral muscles. 
The seventh pedal nerve, 7, arises at the posterior outer margin of the 
ganglion, immediately above the origins of the fifth and sixth nerves, and is 
slightly thicker than either of them. It passes obliquely backward, and, not 
far from its origin, splits into three nearly equal divisions, the first two of which 
are distributed to the anterior and median dorso-lateral regions of the body-wall. 
The posterior division is distributed mainly to the body-wall above and in 
front of the origin of the head retractor muscles, though small branches are 
supplied to that muscle group itself. Several anastomoses are to be found 
with branches from the eighth and ninth nerves, such conditions being in fact 
of fairly common occurrence among the finer peripheral subdivisions of most 
of the nerves to the integument. The distal portion of the seventh pedal nerve 
of the right side also enters into important relations with the nerves from the 
parieto-visceral ganglia, (Plate 3, fig. 2). The three terminal subdivisions, 
