40 



CONARIO-HYPOPHYSIAL TRACT. 



In fact, the enceplialon in the Dibranchiate order resembles 

 that of Vertebrates in the mutual proximity of the " fore " 

 and " hind brains " (fig. 9, ad); so approximated, they are 

 both also protected partially by a cartilaginous case which, 

 with some histological modification, is analogous to, if not 

 homologous with, the vertebrate cranium. 



But the cephalopodic brain retains the invertebrate condi- 

 tion of giving passage to the gullet along the tract or part 

 answering to the third ventricle and thalamencephalon ; only 

 the lateral boundaries or crural tracts are much shorter and 

 thicker than in inferior Mollusks or in Articulates. 



Still it is plain that the nervous mass on one side of the 

 gullet answers to the so-called " supraoesophageal ganglion " 

 (fig. 3, 6), and that on the opposite side to the " subcesopha- 

 geal ganglion " (ib. 3) of lower Invertebrates. 



The latter centre, in Cephalopods, sends off the acoustic 

 nerves (fig. 9, 5'), and is continued into the cords, t, which 

 endow the muscles and skin of the trunk with the motory and 

 sensory powers. A closer resemblance than is usually seen in 

 Invertebrates to the Vertebrate myelon is moreover manifested 

 by the conspicuous gangUons developed on the sensory tracts 

 or cords of the trunk*, and the non-ganglionic continuation 

 of the motory division of the body-cords continued from the 

 Cephalopod's brain. 



From the beginning of the short and thick side-tracts which 

 indicate, if they do not represent, the parts of the vertebrate 

 brain intervening between the "pros-" and " epencephalon " 

 the optic nerves are given off. I need not repeat their well- 

 known characters and developments in relation to the large 

 and complex eyes of the Dibranchiates. 



Beyond the origin of the optic nerves each side-tract termi- 



* ' Anatomy of the Pearly Nautilus,' 4to, 1832, p. 37, pL. 7. fig. 3. 



