144 PEOE. OWEN ON THE HOMOLOGY 



After demonstratiBg, by reference to the Badger, that colour 

 does not indicate the back of an animal, Cuvier proceeds to affirm 

 that naturalists have for the recognition of that aspect a more 

 certain character, viz. the position of the brain : — " lis ont pour 

 reconnattre les dos un caractere plus certain : c'est la position du 

 cerveau"*. 



Now, by the term " cerveau " Cuvier does not here mean the 

 sum of neural expansions usually called " brain," but only one of 

 them, that, viz., which he indicates (as in figs. 7 and 8) by the 

 letter a in both Cephalopod and Mammal ; it is the part which is 

 termed the " supercesophageal mass, ganglion, or pair of gan- 

 glions" in* Invertebrates, and the "cerebrum" or "cerebral 

 hemispheres " in Vertebrates. It is divided, as already remarked, 

 from the " suboesophageal ganglions," completing the totality of 

 the brain in Invertebrates (fig. 4, 3, fig. 7, I), by the extension of 

 the gullet and mouth to the aspect of the body which bears rela- 

 tion to, or corresponds with, that of the main centres of the nervous 

 system — such centres answering, as to the parts they supply and, 

 in Articulates (fig. 4, i), in their continuous extent, to the myelon 

 (fig. 3, i) and ep- mesencephalon (fig. 2, i, 3, 4) in Vertebrates. 

 This homology, however, Cuvier did not admit ; and herein he has 

 had the support of later anatomists. With respect to the myelon 

 — "moelle epiniere" — marked t t in his diagram f, he expressly 

 states that it is peculiar to the type of structure exemplified in 

 his figure A (of the Quadruped)^. But no evidence is adduced 

 against the homology of the elongate moto-sensory tract, or 

 neural axis, in Articulates, and the elongate moto-sensory but 

 seemingly non-ganglionic tract, or neural axis, in Vertebrates, 

 save their difierent relative positions in a standing or walking 

 Badger or Beetle. Cuvier assumed, as Gegenbaur and other ana- 

 tomists have done, that the surface or aspect of the body in pro- 

 gressive motion determines the homology of such surface, and 

 that the surface nearest to which lies the neural axis in Articu- 

 lates answers to that which is furthest from such axis in Verte- 

 brates. But there are both Vertebrates and Invertebrates in 

 which, during progressive motion^, neither the neural nor the 

 hsemal surface is downwards or next the earth. 



* Tom, cit. p. 251, t Tom. cit. pi. xii. 



\ " 1 1, la moelle epiniere propre au Mammifere," torn. cit. p. 257 (referring 

 to his subject as a representative of a Vertebrate animal). 



