2l8 



ZOOLOGY 



of cartilage is in the head. Here there is a cephalic cartilage 

 of complicated form, which is pierced by the oesophagus. It 

 ensheaths the chief nerve ganglia, the ear is embedded in 

 it, and it forms two recesses which lodge the eyes. Another 

 portion affords some support to the bases of the arms, and there 

 is also a iiat piece situated in the neck known as the nuchal 

 plate. 



The chief nerve ganglia are aggregated round the oeso- 

 phagus, close behind the buccal mass, and are embedded in the 



Flo. 128. — Lateral view of the nervous centres 

 and nerves of the right side of Octopus vul- 

 garis. From a drawing by A. G. Bourne. 

 After Lankester — Zoological Articles re- 

 printed from the Encyclopcedia Britannica. 



9. 



10. 



Cerebral ganglion. 



The optic nerve. 



Pedal ganglion giving nerves to arms. 



Pleuro-visceral ganglion. 



Right visceral nerve. 



Riglit stellate ganglion of the mantle, con- 

 nected by a nerve to the pleural portion 

 of 4. 



Branchial branch of 6. 



Olfactory branch of 5. 



Buccal ganglion. 



Buccal mass. 



cartilaginous skeleton. The cerebral ganglion on the dorsal 

 side of the oesophagus gives off a pair of nerves which end in 

 the superior buccal ganglion, from which a pair pass to 

 the inferior buccal ganglion, both lying on the surface of the 

 buccal mass. In connection with these ganglia there is a well- 

 developed stomatogastric system. Laterally each cerebral 

 ganglion is continued into two very stout optic nerves ; 

 these expand into the optic ganglia, situated at the back 

 of the eye. 



The cerebral ganglion gives off two circum-oesophageal com- 

 missures, which pass down to the nervous mass on the ventral 

 surface of the oesophagus. This mass is composed of three 

 ganglia very much fused together. Anteriorly lie the pedal 



