550 



CEPHALOPODA. 



collar of the Nautilus, are notwithstanding 

 indicated in a manner not to be mistaken, 

 by the origins of the nerves which it sends 

 off, and by the chords which bring it into 

 communication with the cerebral mass above. 



We shall now briefly mention the points in 

 which the brain in other Dibranchiata differs 

 from what we have described, after careful 

 examination of this part in the Cuttle-fish. In 

 the Poulp, the brain or supra-cesophageal mass 

 is divided, according to Cuvier, into two parts, 

 an anterior (a, Jig. 233), which is of a flatter 

 and squarer figure and of a whiter colour, 

 compared by Cuvier to the cerebrum, but 

 which seems to be the pharyngeal ganglion 

 more closely approximated to the brain than 

 in the Sepia : and a posterior globular mass 

 ( b), of a grey colour, which he compares to 

 the cerebellum ; the optic nerves (c) are much 

 smaller than in the Cuttle-fish, and do not 

 support the small spherical bodies which exist 

 in the Cuttlefish and Calamary. 



Fig. 233. 



V 



Brain and nerves of the Octopus vulgaris. 



The brain of the Argonauta does not present 

 a rounded form above, but when seen from this 

 aspect, is composed, as in the Octopus, of an 

 -anterior white oblong band, flattened trans- 

 versely, and of a posterior raised convex semi- 

 lunar mass, which terminates behind in a semi- 

 lunar border, the extremities of which are con- 

 tinued directly to form the posterior collar of 

 the asophagus. 



The nerves of the arms proceed from the 

 anterior and inferior subcesophageal ganglions 

 (dyfig. 233), corresponding in number to the 



parts they supply, viz. eight in the Octopoda* 

 and ten in the Decapoda. But, according to 

 Rathke", the Loligopsis offers an exception, the 

 nerves of each lateral series of arms being con- 

 tinued for a short distance from the brain as a 

 single pair. In the Poulp, the eight nerves 

 (e, e,fg. 233) glide along the inner surface of 

 the basis of the feet, which they penetrate re- 

 spectively, running with the great artery in 

 their substance, and forming, as Cuvier has 

 described, a series of closely approximated 

 ganglions, corresponding to each pair of suck- 

 ers, and sending off radiated filaments. In the 

 Genus Eledone, where the arms are narrower, 

 and the suckers are arranged in a single series, 

 the ganglia are relatively smaller. 



In the peduncles of the Decapoda the nerves 

 are continued of a simple structure as far as the 

 acetabuliferous extremities, where they become 

 enlarged and gangliated. 



Before forming the ganglionic enlargements 

 in the ordinary arms, each brachial nerve gives 

 off two large chords, one to each side, which 

 traverse the fleshy substance of the base of the 

 feet to join the two corresponding branches of 

 the contiguous arms ; the eight nerves are thus 

 associated by a nervous circle (f,f, jig. 233), 

 which subdivides into two, and forms a small 

 loop at each chord. 



Behind the origin of the brachial nerves, the 

 large infundibular nerves, a single pair (g, 

 Jig. 233), are given off. The small acoustic 

 nerves (h) arise below and behind the 

 nerves of the funnel, from the nervous sub- 

 stance that effects, as it were, the junction of the 

 two oesophageal collars below. Next arise the 

 large visceral nerves (14,^.232,233), which, 

 after distributing filaments to the muscles of 

 the neck, descend parallel and close to one 

 another behind the vena cava, give off from 

 their inner sides the small filaments which con- 

 stitute the plexus upon the vein; they then 

 diverge from each other towards the root of 

 each gill, where they divide into three princi- 

 pal branches : one of these dilates into an 

 elongated ganglion (c,Jig. 232), and enters the 

 fleshy stem of the branchia; the second de- 

 scends to the bottom of the sac ; the third 

 passes to the middle heart. The plexus pre- 

 viously formed upon the vena cava receives 

 additional filaments from the two latter bran- 

 ches ; and a large sympathetic ganglion is 

 formed, which is attached to the parietes of the 

 stomach, near the pyloric orifice.* 



The most important and interesting nerves are 

 the two largeones,(13,13,/gs.232, 233,)which 

 arise from the posterior and lateral surface of 

 the subcesophageal mass, and extend outwards, 

 downwards, and backwards, perforating the 

 shell muscles, and forming upon the inner 

 parietes of the mantle the large stellated gan- 

 glion ( d, d,Jig. 232), from which the nerves of 

 the mantle are derived. In the Octopoda the 



* See Brandt Medicin. Zoolog. a. a. O. S. p. 309, 

 tab. xxxii. fig. 23, who first described this ganglion 

 in the Sepia, and Jacob's figures of the Anatomy of 

 the Octopus Vulgaris, pi. xv. fig. 7 ; pi. xiii. figs. 

 2 & 3, in Fertissac's Monograph on Cephalopods, 

 fol. 



