IV. OF RANA PIPIENS. 13 



anterior limit of the triangular opening of the fourth ventricle, and beneath it 

 may readily be seen the passage from the fourth to the third ventricle. Attached 

 to its posterior edge, and formed by the folding of the pia mater, is a vascular 

 valve or plexus, which completely covers in this cavity. According to R. Wagner,* 

 the cerebellum " consists, in naked Amphibia and Ophidia, of a hollow medullary 

 layer." In the dissections of Frogs which I have made, I have in no instance 

 been able to verify this statement ; for it has always presented itself in the form 

 of a solid body, though the central portion is more transparent than the cortical. 



The low degree of the development of the cerebellum in Frogs naturally suggests 

 to us an inquiry as to the nature of its functions, and likewise leads to the con- 

 clusion, that, whatever those functions are, they must, on analogical grounds, be 

 supposed to have a low state of activity in comparison with the same organ in those 

 animals in which it is proportionally more largely developed. The low develop- 

 ment of this organ in Frogs and Cyclostome Fishes is certainly at variance with 

 either of the more generally received theories entertained by physiologists of the 

 present time ; namely, those of Gall and Spurzheim on the one hand, and of Flou- 

 rens on the other. It would be difficult to reconcile either of them, or perhaps any 

 existing theory, with numerous other facts afforded by comparative anatomy, all 

 of which tend to show a vast disproportion, at least, between the size of the cere- 

 bellum and the activity of the functions of which it is alleged to be the seat. 

 As regards the theory of sexual instinct, this function is certainly not less strongly 

 manifested in the Lamprey than in ordinary Fishes, as the Trout or the Herring ; 

 yet how widely different is the relative size of the organ in the two ! Professor 

 Owen has contrasted Lampreys with the Sharks, showing that the difference in the 

 cerebellum of these animals is entirely disproportioned to any known distinction 

 relating to the sexual instinct.f The well-known experiments of Leuret, though 

 perhaps less extended than could be desired, are, as far as they go, wholly opposed 

 to the hypothesis. 



Although the experiments of Flourens and his followers tend to show a con- 

 nection between locomotion and the cerebellum, disturbance of the former usually 

 attending injuries inflicted on the latter, yet his theory that the cerebellum co- 

 ordinates muscular motions is opposed by numerous anatomical facts, as well as by 

 some of the results of pathology ; for out of ninety-three cases of lesions of the 

 cerebellum, Andral found but one to sustain the theory of Flourens. The necessity 

 for coordinating motions in Frogs, animals moving with four legs, is as great as, if 

 not greater than, in most Fishes, moving solely by the aid of the vertebral column, all 

 their principal motions being produced by its flexion and extension. In Petromyzon, 

 with its still more rudimentary cerebellum, we have the power of coordination as 

 great, and muscular activity as intense, during the breeding season at least, when they 

 stem the most rapid currents and ascend falls of water, as in the Trout, the Sucker, or 

 the Pike, which have the cerebellum proportionally much longer. We will take one 



* Elements of the Comparative Anatomy of the Vertebrated Animals, p. 150. 

 t Lectures on Comp. Anat. and Phys. of Vertebrated Animals, Part. II. p. 188. 



