The nuclei of the vestibular nerve of the red kangaroo, Megaleia rufus.

The preceeding account describes vestibular nuclei of the kangaroo which conform to the general mammalian pattern. Certain pecularities such as subdivisions of the medial vestibular nuclei are reported but cannot be assigned functional importance. The four major vestibular nuclei and the cerebellum receive vestibular root fibers in like manner as in other mammalian brains. The nuclear patterns and the secondary connections of the vestibular complex in the kangaroo are likewise consistent with those described in other mammals. This is so evident from the description of these regions in the kangaroo and the reports in the literature that the statement needs no further documentation. However, there are certain differences which are significant. Unusual size and/or differentiation of a center, together with an increase in the projection path arising from it, is often reflected in the behavioral patterns of the animal. Thus the lateral vestibular nucleus and the ventrolateral vestibulospinal tract are conspicuously large in the kangaroo in which the methods of locomotion and the manner in which he fights must require frequent orientation in space. It is obvious that the locomotion capabilities of the kangaroo are in large measure due to his well developed vestibular complex and its descending connection. Studies of the sort represented here, then, emphasize the specializations in certain systems and provide information with regard to the interrelations between the anatomic patterns and functional specilization in these systems. They also supplement our knowledge of the course of differentiation within the mammalian phylum. It is to be noticed that specialization at a given level may occur at any place in the evolutionary scale but cephalization is an indication of a relatively progressive development from lower to higher forms.