618 LECTURE XXIV. 



have already intlicated the parts which seem to represent the crura 

 of the cerebrum ; they unite with that large sub-oesophageal nervous 

 mass, which, since it gives origin to the brachial nerves or the 

 homologue of the fifth pair, to the acoustic and respiratory nerves, 

 and to those two large moto-sensory columns which resemble in 

 their structure, position, and distribution, the spinal chord of the 

 Vertebrata, must be regarded as the representative of the medulla 

 oblongata : it is obviously the part of the nervous centre which is 

 most intimately connected with the vitality of the animal, and which 

 is therefore here, as in the higher animals, the deepest seated and 

 best protected part of the nervous system. 



The disposition of this system determines the surfaces of the body 

 of the Cephalopod which correspond with those of the fish. The 

 nervous centre (a, fig. 223.), in which, from its comparative in- 

 dependence of, or indirect connection with, nerves, sensations are 

 most probably raised into ideas, denotes the dorsal aspect, to which, 

 as in tlie Vertebrata, the term " neural " would not be inapplicable, 

 regard being had to the value of the brain-mass marking the aspect, 

 and to the corresponding position of the chief nerve-trunks of the 

 body. Thus, in the Argonaut {fig. 220.), b, e, a mark the dorsal 

 aspect, i the ventral one, d the anterior part, and c the posterior 

 part. The homology of the cerebrum («, fig. 223.), with the 

 reduced super-oesophageal mass («, fig. 215.), determines unequi- 

 vocally the true dorsal or neural aspect in that and all inferior forms 

 of mollusk. But the inconstancy of the position of the heart and 

 chief vascular developments for breathing, renders the terms " neural " 

 and " hasmal," as now accepted for the Vertebrata, too arbiti-ary or 

 contradictory for the Mollusca. 



The integument is remarkable in several of the naked Cephalopods 

 for its irregular surface, which seems designed to increase its natural 

 sensibility : in some, it is provided with flattened crenate processes ; 

 in others it is beset with branched papillae ; in a third with simple 

 obtuse papillae ; in a fourth with pointed tubercles ; all which pro- 

 jections may serve to warn the animal of the nature of the surfaces 

 with which it may come into contact. The margins of the acetabula 

 and the attenuated flexile extremities of the arms which support 

 them doubtless possess a delicate sense of touch. The fringed 

 circular lip presents another example of the dermal covering modified 

 to be the seat of this sensation. 



The tongue is as highly developed for the exercise of the sense of 

 taste in the Dibranchiate Cephalopods as in the Nautilus. In 

 Onychoteuthis {fig. 225.), the fleshy part of the tongue is "produced 



