70 



the second (fig. 76, b and e). The fourth pair run 

 forwards and outwards over the wall of the sinus. Thus 

 they cross over the buccal nerves which run forwards and 

 inwards (fig. 76, J. and B. N.). Each of the two gives oft 

 two branches, an inner and an outer. The three branches 

 thus obtained now run over the wall of the sinus to end 

 in the lip. 



A. 4 Buccal Nerves. — These are two nerve- much 

 stouter than the labial. Running from the outer anterior 

 alible of the cerebral ganglion each nerve pierces the 

 anterior cranial wall, and then runs inwards towards the 

 sub-oesophageal ganglion (PI. VIII, fig. 72. B.N.). 

 Arriving at the posterior lateral wall of the buccal mass, 

 this nerve divides into three branches (fig. 72. I).. M. and 

 V.). Of these, the most dorsal runs up to the sub- 

 iphageal ganglion, the median ends in branches in 

 the buccal wall, while the ventral one curves downwards, 

 and ends similarly in the wall of the buccal mass. The 

 innermost branch given off from this ventral nerve runs 

 towards its fellow from the other side and meets it 

 just below the initial part of the radula sac, -welling 

 here to form a small, oval sub-radular ganglion H<r. 72, 

 r. b.). 



Ophthalmic Nerves. To see these it is best to 

 expose the eyes from the dorsal surface by dissecting 

 away the -kin and superficial muscles from the back of 

 tin' head (PI. IX. fig. 74. A'... Thus the muscle- which 



dorsally cover the brain case and the bases of the arms 

 are also exposed (fig. 74. b 1 and a). There are three 

 groups of ophthalmic nerves on each side: — (1) three 

 anterior superior, (2) one posterior superior, and (3) three 

 inferior. 



A. (5) The Anterior Superior Ophthalmic are three 

 fine nerves, which arise dorsal to the origin of the optic 



