§^ 239, 240. THE CEPHALOPODA. 277 



With Nautilus, there are two large, particular muscles, which arise from 

 the under surface of the cephalic cartilage, and extend, divergingly, back- 

 wards; they serve, by means of a horny plate, to fix the animal to the 

 internal border of the shell/'-'* 



CHAPTER IV, 



NERVOUS SYSTEM. 



§ 239. 



The nervous system of the Cephalopoda attains a very high degree of 

 development. Its central portion, especially, quite resembles the brain of the 

 Vertebrata, in the extraordinary increase of its ganglionic substance, and 

 by the presence of a cartilaginous cavity containing it, comparable to a 

 cranium. This cavity is incomplete, it is true, but at its anterior part 

 where the cartilaginous substance is wanting, it is closed by a tendinous cel- 

 lular tissue which takes the place of a Dura mater. 



The brain itself, which is far from filling the cavity of the cephalic carti- 

 lage, is enveloped by a fibrous membrane, which sends off sheaths to the 

 nerves which leave the brain and traverse, in diiferent places, the cephalic 

 cartilage. The cavities remaining between the brain and this cartilage are 

 filled with a fat-like liquid. 



The primitive nerve-fibres are straight, finely granulated, and bound to- 

 gether into fasciculi of variable size by a very distinct neurolemma.^'* The 

 long and oval corpuscles which are often found in abundance between them, 

 belong probably to the neurolemma. 



§ 240. 



The central mass of the nervous system, with the Cephalopoda, forms also 

 an cesophageal ring, which consists of a superior and an inferior ganglionic 

 mass connected by lateral commissures. The superior jJortion is small and 

 sends some delicate nerves to the parts of the mouth. The inferior portion 

 on the contrary, is very large, and extends along the sides of the oesopha- 

 gus in order to be directly continuous with the broad commissures. The 

 olfactory, and the two optic nerves arise from the lateral portions of this 

 ganglion, while the auditory nerves have their origin from its inferior 

 surface. 



From its anterior border pass ofi" four or five pairs of large nerves to 

 the arms, and, also, others to the muscles of the head. From its posterior 

 border arise small nerves for the funnel, and also two large trunks for the 



9 Owen, On the Nautilus, p. 17, PI. IV. fig. 2, (Muller^s Arch. 1846, p. 128), the histological coui- 



k., or Isis, p. 15, or Ann. d. Sc. Nat. p. lua, PI. II. position of the ganj-'Ha with the Cephalopoda i3 very 



fig. 3, k., and yalenciennes, loc. cit. p. 208, PI. remarkable. They have here found very lar.e 



XI. fig. 4, P. ganglionic globules, of even one-tweuty-tifth o n i 



1 KoUiker, Entwickelung. d. Cephalop. p. 79. inch in diameter, and containing, each, sever;! 



According to the researches of Lebert and Robin nuclei. 



24 



