$$ 239, 240. THE CELAALOPODA. QTT 
With Nautilus, there are two large, particular muscles, which arise from 
the under surface of the cephalic caftilage, and extend, divergingiy, 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 different 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 portion 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 cesopha- 
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 off 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, Pl. IV. fig. 2, (Miiller’s Arch. 1846, p. 128), the histological com- 
k., or Isis, p. 15, or Ann. d. Sc. Nat. p. 103, Pl. II. position of the ganglia with the Cephalopoda is very 
fig. 3, k., and Valenciennes, loc. cit. p. 268, Pl. remarkable. They have here found very large 
XI. fig. 4, P. ganglionic globules, of even one-twenty-fifth of an 
1 Kélliker, Entwickelung. d. Cephalop. p. 79. inch in diameter, and containing, each, several 
According to the researches of Lebert and Robin nuclei. 
