616 LECTURE XXIV. 



ganglion, fi'om which the nerves of the feet and tentacles arise. 

 Two broader bands descend from the super-cesophageal mass behind 

 the preceding, and form, by a like enlargement and union, the 

 posterior oesophageal body, which blends laterally with the anterior 

 one, and forms with it a large mass with a central perforation. Four 

 short and slender chords, two of which (e) are continued from the 

 anterior apices of the optic lobes, and two from the anterior sub- 

 cesophageal lobes, converge forwards and unite to form a round 

 flattened ganglion {g), which is closely applied to the back part of 

 the fleshy mass of the mouth above the pharynx, from wliich are sent 

 off the nerves to the retractors of the mouth. Two filaments from 

 the pharyngeal ganglion descend to join a pair of ganglions below 

 the pharynx, homologous with the labial ganglions of the Nautilus, 

 and the buccal ganglions of Gastropods. The nerves of the arm 

 (f, f) proceed from the anterior sub-oesophageal ganglion, and 

 correspond in number to the organs which they supply, being eight 

 in the Octopoda, and ten in the Decapoda: the corresponding nerves 

 are much more numerous in the Nautilus. In the Loligo they have ■ 

 a double origin, the anterior sub-oesophageal mass being divided into 

 an anterior and posterior portion, and each brachial nerve deriving a 

 I'oot from both centres, which may have distinct functions, one 

 motory, the other sensory.* In the Octopus the brachial nerves 

 pass along the inner surface of the base of the arms before they 

 penetrate the axial canals. As soon as the acetabula begin to be 

 developed, a series of closely approximated ganglions are formed 

 upon the brachial nerves, of which some of the longitudinal fibres 

 pass over the ganglions. Before the ganglionic enlargements 

 commence, each brachial nerve in the Octopus gives off two large 

 branches, which traverse the fleshy substance of the base of the arms 

 to join tlie two corresponding brunches of the contiguous nerves 

 which ai'e thus associated together for consent of action by a 

 nervous circle. 



The infundibular nerves arise behind the origin of the brachial 

 ones. Posterior to these the small acoustic nerves are given off from 

 the sub-ojsophageal mass. The delicate motores oculi arise from the 

 upper part of the lateral connecting bands of the infra- and sui5ra-oeso- 

 phageal masses, which may be compared with the crura cerebri, as the 

 nerves in question obviously answer to the third pair in the Vertebrata. 

 Tiie nerves going to the cavities, supposed to be olfactory, arise close 

 to the optic nerves. The nerves which correspond to those of the 

 shell-muscles of the Nautilus, form a single large pair {m, m), which 



* CCLXXVIII. p. 2. 



