44 CLASS XIV. 



The comparison with tfye brain of reptiles, and especially the 

 history of development of the brain in higher vertebrates, which is 

 most perfectly known to us in the embryo of the bird, induces us to 

 recognise in the hollow lobes in front of the cerebellum in fishes 

 the union of the corpora quadrigemina and of the space for the third 

 ventricle of the brain (lobi optici}. If this be right, then fishes have 

 no corpus callosum, unless a transverse communication between 

 these lobes, which some writers regard as such, deserves that appel- 

 lation. As little is there a pons Varolii on the inferior surface in 

 front of the m,edulla oblongata. In addition to these two negative 

 characters of the brain of fishes, the small development of the 

 cerebrum (anterior brain) in comparison with that of the optic lobes, 

 may be assigned as distinguishing the brain of fishes from that of 

 reptiles and birds. Those parts of the brain, which in man are 

 covered above by the hemispheres of the brain, are here placed 

 behind one another as middle and posterior brains 1 . 



The spinal nerves arise, as in the rest of the vertebrate animals, 

 by two roots, one from the posterior or upper, and one from the infe- 

 rior strand of the spinal cord. The posterior roots of these nerves, 

 which swell into a ganglion, are the sentient roots, the anterior 

 the motor roots 2 . As to the cerebral nerves, the common type of 

 the vertebrate animals prevails in fishes also, and, with the excep- 

 tion of the nervus hypoglossus and accessorius Willisii, all the pairs 

 of nerves that spring from the human brain, occur in almost all 



1 Whenever a glandula pinealis is found, as is the case in some fishes, it is situated 

 behind the anterior and in front of the middle lobes of the brain, and thus affords an 

 additional proof that the middle lobes of the brain do not correspond to the cerebrum. 

 See, on the brain of fishes, HALLER Elem. Physiol. iv. 1766, pp. 591 596; and more 

 fully in VerJiandelingen van die Hollandsche Maatschappij der Wentensch. Haarlem, x. 

 i, pp. 314 386; A. ARSAKY Dissert, de piscium cerebro et medulla spinali. Halse, 

 1813 (new edition by MINTER, Leipzig, 1836, 4to); CUVIER Hist. not. des Poiss. T. 

 pp. 415 434; C. M. GOTTSCHE Vergleichende Anatomic des Gehirns der Grdtenfische, 

 MUELLER'S Arckiv, 1835, s. 244294, 433486, Taf. iv. vi. Kespecting the reduc- 

 tion of the brain of fishes to the common typus, the most important questions are 

 investigated by MUELLER Physiologie, I. (third edition, 1838, s. 824 829). 



2 We presume that this physiological truth, of which the discovery is due to C. 

 BELL, is known to the reader ; it applies to all vertebrate animals, and is to be regarded, 

 especially since MUELLER'S experiments on frogs (Physiologie, I. 3tte Auflage, s. 651 

 653)* as a we ll established general proposition in our still limited knowledge of nervous 

 function. 



