NERVOUS SYSTEM. 585 



different portions of which, nerves serving very different offices take 

 their origin. 



(1567.) In Nautilus the nervous system has been most minutely and 

 critically examined ; and the important deductions to which the re- 

 searches of Professor Owen point, relative to the analogies that may be 

 traced between the encephalon of these creatures and the brain of higher 

 animals, have served to attach an interest to the study of this part of 

 the economy of the CEPHALOPODA which has scarcely as yet been suffi- 

 ciently appreciated by physiologists. 



(1568.) In the Nautilus Pompilius, the supra- cesophageal ganglion of 

 the GASTEROPODA is represented by a thick round cord of nervous matter 

 (fig. 291, l), which is in communication with two nervous collars (3 3, 

 4 4) that surround the oesophagus, and likewise with two large ganglia 

 (2) from which the optic nerves take their origin ; but in the Cuttle- 

 fish the same portion of the nervous system (fig. 294, a) is much more 

 largely developed, and presents a ganglionic mass of considerable size. 

 If we inquire the reason of this want of correspondence in magnitude 

 presented by the same organ in these two cases, we must necessarily 

 examine the relations in which this part of the brain stands with other 

 circumstances in the economy of the two animals in question ; and we 

 perceive, as Professor Owen has most satisfactorily demonstrated*, that 

 the brain is here developed in accordance with the relative complexity 

 of the organ of vision, and also with the perfection of the locomotive 

 faculties possessed by the Cephalopods under consideration. With the 

 exception of sundry small twigs given off to the mouth and pharynx, 

 the optic nerves (fig. 291, 2 ; fig. 294, e) are the only ones derived 

 from this part of the encephalon ; and, as we shall afterwards see, both 

 the simply- constructed eye of the Nautilus and the complicated visual 

 organs of the Sepia are correspondent to the development of the supra- 

 oesophageal brain ; so that consequently the latter may, with every 

 show of reason, be looked upon as the representative of the optic lobes 

 found in the encephalon of fishes f, and the analogue of the bigeminal 

 bodies in the brains of the higher Yertebrata. 



(1569.) The ganglia connected with the inferior aspect of the supra - 

 O3sophageal mass form two distinct collars embracing the ossophagus, 

 an arrangement of which we have already met with an example in Clio 

 bor'ealis among the Pteropod Mollusca. In Nautilus, the anterior ring 

 of nervous substance, which no doubt ought rather to be considered 

 as an agglomeration of ganglia than as a simple ganglionic mass, 

 gives off nerves, 1st, to the ophthalmic tentacles (fig. 291, 5) ; 2ndly, 

 to the digital tentacles (6) ; 3rdly, there arises, from near the ventral 



* Descriptive and Illustrated Catalogue of the Physiological Series of Comparative 

 Anatomy contained in the Museum of the Royal College of Surgeons of England, 

 vol. iii. part 1. p. 187. 



f Cyclopaedia of Anatomy and Physiology, art. CEPHALOPODA. 



