360 DE. G. ELLIOT SMITH ON 



the mesial plane. These are known as its j)ecluncles. The superior cerebellar peduncles 

 issue from the mesencephalon and proceed directly backward, at a distance of 9 mm. the 

 one from the other. They soon meet the middle peduncles extending dorsally from the 

 pons and the fibres of the inferior peduncles which ascend from the medulla oblongata and 

 spinal cord. Together the three peduncles of each side form a large and massive column- 

 like support for the cerebellum, and hence the combined mass may be called the cohimna 

 Ge7'ehcUi. The fourth ventricle is a broad and very shallow cleft which lies upon the 

 expanded dorsal surfaces of the region of the pons Varolii and the upper open part of 

 the medulla oblongata. Its anterior part is placed between the two parallel superior 

 peduncles of the cerebellum, and is roofed by the medullary velum which stretches 

 between these peduncles. The posterior part of the ventricle is triangular in outline, 

 the lateral angle of the triangle extending widely behind the columna cerebelli on each 

 side and forming the lateral recess. In the floor of this lateral recess we find the 

 crescentic tuherciilum acasticmn kderale. On the mesial side of this, we find in the 

 floor of the fourth ventricle a larger i-ounded and very prominent mass of grey matter, 

 which we may call the tuherculum acusticum mediale (fig. 27). In the writings of 

 different anatomists the nomenclature of this region is often responsible for much 

 ambiguity. The tei'm " tuberculum acusticum " is commonly applied to that body which 

 I have distinguished by the adjective " laterale," and the name " trlgonum' ncusticum " 

 to my " mesial tubercle " ; but these terms are very confusing. For the difference in the 

 name leads writers to regard the tubercle sometimes as part of the trigone, at other times 

 as a separate body, or even to confuse the trigone with the tubercle. For the sake of 

 clearness of description I have introduced the qualifying adjectives " laterale "• for the 

 tubercle which is probably cochlear, and " mediale " for that which is probably vestibulai-, 

 and called them both " tubercle." 



In all the Edentates the features of this region are practically constant and call for no 

 fuller description. 



The Cerebellum. 



We might with almost equal justification begin the description of the cerebellum in 

 the Edentata at the present time with the same remarks which Pouchet emjiloyed in 

 introducing the same subject thirty years ago. But if Pouchet found reason in his time 

 to deplore the obscurity which anatomists had allowed to enshroud the comparative 

 anatomy of this important organ, we at the present day have infinitely more reason to 

 bemoan our ignorance. Por while the subject of cerebellar morphology has received 

 little more illumination than it had in Pouchet's day, the feverish activity which has 

 prevailed in all other fields of neurological investigation has thrown such a clear light 

 upon the anatomy of the rest of the nervous system that by contrast our ignorance of 

 cerebellar morphology seems to-day greater than ever. 



When this investigation was begun two years ago, I fovmd it necessary to study for 

 myself the comparative anatomy of the cerebellum in an extensive series of vertebrates 

 before it was possible to intelligently appreciate the Edentate types of cerebellum, and 

 understand the morphological plan to which these types conform. Perhaps the greatest 



