320 



LECTURE XXIII. 



contrivance is manifested to prevent the compression of the nerves 

 and vessels in the muscular system of the ninety proboscides of the 

 Nautilus. 



For the special account of the myology of the Nautilus, which 

 includes the muscles of the oral sheath and its digitations, those 

 of the labial processes and mouth, those of the infundibulum, those 

 for adhesion to the shell, those of the mantle, those of the tongue, 

 the fibres of the tunic inclosing the liver and stomach, and the 

 muscles of the organic system, I must refer to the published mono- 

 graphs on the anatomy of this animal.* 



The principal masses of the nervous system of the Pearly Nautilus 

 {fig* 130.) are concentrated in the head. The supra-oesophageal 



part, or brain (a), presents the form 

 of a short, thick, transverse, round 

 chord or commissure, connected at 

 each extremity with three gangli- 

 onic masses. The middle and supe- 

 perior of these {h) supplies the eye 

 and the inferior hollow tentaculiform 

 organ : the anterior and inferior 

 ganglion (c) meets its fellow below 

 the oesophagus ; the posterior gan- 

 glion {d), in like manner, joins that 

 of the opposite side and forms a 

 second and posterior oesophageal 

 ring. The nerves given off imme- 

 diately from the supra-oesophageal 

 mass supply the muscular and other 

 parts of the mouth, and have small 

 pharyngeal ganglions developed up- 

 on them. The anterior oesopha- 

 geal ring gives off principally the 

 nerves to the tentacula (/,/), and 

 the two median ones (^) are con- 

 nected with a ganglion (/^), which 

 supplies the tentacula of the inferior 

 labial processes and the lamellated 

 Nervous System. Nautilus. organs on that part of the Oral 



sheath. The tentacular nerves are continued, like those of the arms 

 in the higher Cephalopods, along the middle of the tentacle, at- 



* Memoir on the Pearly Nautilus. 

 Museum d'Histoire Naturelle. 1839. 



4 to. 1832. Valenciennes, Archives du 



