THE BRAIN IN THE EDENTATA. 329 



Edentata. We find a deep sulcus beginning just in front of the termination of the 

 hinal fissure, and following a course upward and then forward, pai'allel to the corpus 

 callosum. Before reaching quite as far as the genu this deep sulcus stops as such, 

 but it may be continued as a shallow furrow obliquely upward on the dorsal surface. 

 To this Krueg has applied the name ^'fssura splenialis,'" from its relation to the splenium 

 corj)oris callosi *. An independent sulcus pursues a course parallel to the anterior 

 extremity or gemt of the corpus callosum, and is hence known as the fssura geii/mlls. 



In the important memoir of Krueg to which reference has just been made, the 

 presence and essential uniformity in the arrangement of this splenial sulcus in all the 

 Ungulata is clearly demonstrated by means of a beautiful series of illustrations and a 

 lucid description. Two years later the same investigator earned our further gratitude 

 by showing, in the same clear manner, the existence of an analogous sulcus in a large 

 series of other mammals, including the important order of Carnivoraf. 



From these valuable series of observations we learn that in a very considerable 

 number of widely-separated mammals we find a constant arrangement of sulci cor- 

 responding to those which we have called «' and a" in Myrmecophaxja, and which 

 together form a feature for which Krueg has introduced the term fissura splenialis. 

 We also learn that a genual sulcus surrounds the anterior extremity of the corpus 

 callosum, but its shallowness and inconstancy point to the fact that it is of considerably 

 less importance than the splenial sulcus. 



The high importance of the splenial sulcus is shown not only by its depth, its constancy, 

 and its well-defined features, but also by the fact that it is the first pallial fissure to make 

 its appearance in the Cat and probably also in the Sheep %. In the foetal Cat it begins 

 as a small arcuate sulcus behind the corpus callosum, which is analogous to the permanent 

 condition of this sulcus in Dasj/pus ^. As the hemisphere grows, the sulcus splenialis 

 extends forward. In the develo^wuent of this sulcus in the Edentata it is highly probable 

 that a similar mode of development would be found in Myrmecophaga and Orycteropjus 

 for the posterior vertical part of the sulcus which we have called a! is deeper than the 

 rest, and in Orycteropus, if not in others, it is " complete." It is this postero- ventral 

 part of the sulcus, m.oreover, which is the most constant. We have already had 

 occasion to observe the constancy of its relation to the rhinal fissure not only in 

 Orycterop'us and Myrmecophaga, but also in the JBradypodldcc and possibly in the 

 Dasypodidcs. 



In many families of Marsupials we find a sulcus upon the mesial surface of the hemi- 

 sphere, which presents the typical relationship to the fissura rhinalls which characterizes 

 the sulcus splenialis. In many Marsupials (e. g. Phascolarctos) this sulcus,is quite short, 

 and is confined to the situation corresponding to that in which the early splenial sulcus 



* Julius Krueg, " Ueber die Furchung der Grossliirnrinde der Ungulateu," Zeitsch. f. wiss. Zool. Bd. sxxi. 

 p. 308. 



t Julius Krueg, " Ueber die Furehung auf der Grossliirurinde der Zonoplaccnlalen Siiugethiere," Zeitseh. f. wiss. 

 Zoologie, Bd. 3xsiii. 



+ Vide Krueg, o/j. cit., Zeitsch. f. wiss. Zoologie, Bd. xxxi. & xxxiii. 



§ Vide Krueg, op. cit., Bd. xxxiii. Taf. xxxiv. 



