ON THE ANATOMY OF NAUTILUS POMPILIUS. 195 



account, however, as von Jhering's remarks are very brief, while 

 in the construction of his diagram a curious blunder seems to 

 have been made, which has been perpetuated by its being 

 copied by leading text-books. In effect, what he figures as the 

 cerebro-pharyngeal connective is really the forward prolongation 

 of the pharyngeal ganglion, which, uniting with its fellow in the 

 middle line, forms the anterior infra-buccal commissure. On 

 the other hand, the two nerves figured as emerging from the 

 pharyngeal ganglia laterally are the cerebro-pharyngeal con- 

 nectives, of which there are not one, but two, on each side. In 

 fact, by rotating the portion of his figure representing the 

 buccal nervous apparatus through 180° about an axis passing 

 through the pharyngeal ganglia and joining up at the cut ends 

 as indicated above, one gets quite an accurate diagram. No 

 doubt v. Jhering's slip arose through dissecting and figuring 

 this part of the nervous system after the buccal mass had been 

 removed from its connection with the animal. 



The cerebro-pharyngeal connectives are two thick nerve- 

 trunks on each side, taking their origin from the adoral border 

 of the supra-oesophageal nervous mass. Enclosed in a dense 

 sheath of connective tissue, they pass to the sides of the buccal 

 mass. For the first part of their extent their course is highly 

 sinuous, a character probably to be connected with the pro- 

 trusibility of the buccal mass and the consequent very variable 

 distance between it and the fixed circum-oesophageal parts of 

 the nervous system. Pursuing a slightly convergent course the 

 two connectives reach the lateral aspect of the buccal mass, and 

 there unite in the pharyngeal ganglion (fig. 4, ph. g.) — a trian- 

 gular structure with its apex directed towards the mouth — and 

 another of its angles external. It lies on the muscles of the 

 buccal mass immediately beneath the skin. 



The two pharyngeal ganglia are connected to one another 

 by a longer anterior and a shorter posterior commissui'e, on the 

 course of the latter being the slightly swollen " buccal ganglia." 

 The anterior commissure (fig. 4, ant. com.), figured by v. Jhering 

 as cerebro-pharyngeal connective, is a flattened band nearly 

 1 millimetre in breadth, and pursuing a n -shaped course 



