IV. OF RANA PIPIENS. 9 



other. This complete separation of these lobes in the animals above referred to, is 

 certainly an interesting anatomical feature, as bearing upon the physiology of the 

 parts, and tending to prove the existence of complete duality of function ; for it 

 can hardly be supposed that two organs so completely separated could be any 

 more mutually dependent than the two eyes or two ears ; each is the seat of its 

 own functions and processes, though the functions of the two sides are doubtless 

 precisely similar. 



The closing up in front of this fissure between the cerebral lobes, by the united 

 olfactory lobes, leaves an opening through the brain from above downwards, and 

 this might at first sight be compared to the ring which transmits the oesophagus in 

 the Invertebrate animals. If this comparison be allowed, it would afford some sup- 

 port to the doctrine, which assumes a homology between the nervous centres of the 

 Vertebrate and Articulate divisions of the animal kingdom. The question of the 

 correctness of such a comparison will necessarily present itself in the course of the 

 following descriptions, and the remarks we have to make upon it may be not im- 

 properly presented here. 



Although frequent attempts have been made to homologize the nervous systems 

 of Vertebrates and Articulates, yet in reality there seems to exist no correct basis 

 on which the alleged homology may rest. Among the earlier advocates of this 

 view were Gall and Spurzheim, but a more able advocate was found in Geoffroy St. 

 Hilaire. Still more recently, the doctrine has been revived, at least in part. In 

 the recent edition of his General and Comparative Physiology, Dr. Carpenter seems 

 to recognize the homology of certain portions, at least, of the nervous systems of 

 Articulates and Vertebrates, though in others he admits simply an, analogy ; after 

 stating that there is nothing in the Articulates homologous with the cerebrum and 

 cerebellum of the Vertebrates, he says, " The first subcesophageal ganglion, which 

 has been likened to the latter (the cerebellum), being really homologous, as the dis- 

 tribution of its nerves abundantly proves, with the medulla oblongata." * In speak- 

 ing of the spinal chord, he says, " It consists of a continuous tract of gray matter 

 inclosed within strands of longitudinal fibres, and it may thus be regarded as anal- 

 ogous to the ganglionic chain of the Articulates." If there be any homology, it 

 seems to us as if the whole nervous system of the Articulates, as far as it is devel- 

 oped, should be homologous with a corresponding portion of that of the Verte- 

 brates. If the subcesophageal ganglion is homologous with the medulla oblongata, 

 that which follows it should be homologous with the spinal chord. There seems 

 sufficient ground for the belief, that all homology between the nervous systems of 

 the two divisions is as much contraindicated, as between their skeletons or their 

 muscular systems. If a true homology existed, we ought at least to have repre- 

 sentatives from the Articulates and Vertebrates, in which the identity would be ob- 

 viously proximate, if not absolute. But as yet there has been described no instance 

 where the spinal chord, structurally considered, is fairly and distinctly represented 

 in the Articulates, nor among Vertebrates any true ganglionic chain with an 



* Gen. and Comp. Phys., 3d edit., p. 1017. 



