8 PROF. OWEN ON CEREBRAL HOMOLOGIES 



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 

 large 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 tlie origin of the optic nerves each side tract termi- 

 nates in a " suboesophageal " mass, divided into two portions and 

 supplying the parts corresponding with those in Vertebrates 

 which send and receive their nervous influences through the 

 " medulla oblongata " (macromyelon) and the " spinal cord " 

 (myelon). 



The dibranchiate horaologue of the supraeesophageal ganglion 

 moreover supports a part of the vertebrate cerebrum, less mani- 

 festly, if at all, shown in other Invertebrates ; it is a superposed 

 mass of a whiter colour than the rest of the encephalic centres,. 

 with an indication of a division into a lateral pair of lobes, and, 

 in Sepio, presenting a subtriangular form with the apex anterior. 

 From the deeper-seated part of the " supraeesophageal " mass 

 are sent off, besides smaller filaments, a pair of nerves, or " crura," 

 which converge and are lost in a more anterior ganglionic mass 

 — the " ganglion sus-buccal," or the superoral ganglion, of Cuvier 

 — which distributes nerves to the delicate membranous folds and 

 processes developed from the interspaces of the cephalic arms^ 

 and to the plicated and papillose lips which surround and project 

 anterior to the beak, and which soft and lubricous parts we may 

 reasonably suppose to receive from their superoesophageal, or 

 cerebral, centres the faculty of judging of the odorous qualities of 

 the substances to be seized by the beak. 



From the anterior portion of the larger " suboesophageal " 

 mass are sent ofi" nerves to the rasping and gustatory organs 

 within the mouth, and the larger nerves which supply the eight 

 cephalic acetabuliferous arms and tentacles. From the pos- 

 terior division of the suboesophageal mass are sent off the moto- 

 sensory nerves of the trunk already noticed, and also visceral 

 nerves *. 



In the Tetrabranchiate Cephalopods the foregoing primary di- 

 visions and functions of the brain are simplified, and so are more 

 clearly manifested. The cartilaginous defensive case protects 

 only the homologue of the " sub-" or, rather, " neuroesophageal " 

 * "^ Memoir on the Pearly Nautilus,' 4to, 1832, p. 37, pi. 7. fig. 3. 



