69 



smaller oval ganglion (fig. 71, o.g.). Cheron termed 

 this the olfactory ganglion, but Zernoff denies its 

 connection with the olfactory organ. 



A. (2) The Olfactory nerves.— The strands of the 

 olfactory nerve are, at their origin, indistinguishable from 

 those of the optic nerve. They lie ventral to these, 

 however, and run along with them to the optic ganglion. 

 Here they separate, and run on as a separate nerve, which 

 is absolutely independent of and unconnected with 

 ('heron's olfactory ganglion (fig. 71, olf. N .). Beyond 

 the separation from the optic nerve it may be seen, 

 running external to the white body, on the internal wall 

 of the orbit (tig. 71, ./■.), where it pierces the wall of 

 the eyeball and then runs over the dorsal posterior wall 

 of the eye to the olfactory pit, which it innervates 

 (PI. IX, fig. 74, olf. N. and olf. P.). 



A. (3) Labial nerves. — These are four pairs of line 

 nerves, which run out from the anterior edge of the 

 cerebral ganglion and innervate the lip (fig. 76, a, b, c, 

 and d). Leaving the cranial cavity, they pierce the 

 membranous wall which closes this cavity anteriorly, and 

 then run over the outer wall of the sinus venosus, which 

 here surrounds the buccal mass, anterior salivary glands, 

 and oesophagus (fig. 70, S. V.). Anterior to the sinus 

 venosus, the)' run over the outer wall of the buccal mass, 

 and so finally reach the lip, where they end in tine 

 branches. The innermost pair of labial nerves (tig. 76, it) 

 leave the cerebral ganglion one on each side of tin; 

 middle line, and running along the outer wall of the 

 sinus venosus, each soon divides into two branches. 

 Reaching the anterior limit of the sinus venosus, each 

 half again gives off several small branches, which end 

 finally in the lip. The second and third pairs have a 

 similar course, the third pair being rather stouter than 



