150 Cincinnati Society of Natural History. 



The girdling fibres of the medulla passing to the cerebellum (or 

 those representing the pons) require more careful study. Our 

 sections suggest that they are of two sorts. First, such as spring- 

 ing from lateral regions of multipolar cells in the medio- ventral 

 portion of the medulla, pass directly dorsad to the decussation on 

 the roof of the fourth ventricle, thence to the cerebellum ; second, 

 those which may have their origin in the same multipolar cells, but 

 pass to the raphe, where they discussate; and then forming bands 

 of fibres corresponding to the pons fascicles of higher vertebrates, 

 pass into the postero- lateral crura of the cerebellum. Both sets of 

 fibres were traced to the median portion of the organ, where they 

 pass through the nucleary zone, radiating to the Perkinje's cells, 

 whose processes connect with the superficial fibre zone. No infor- 

 mation concerning tracts connecting the medullary nuclei with the 

 superficial fibre zones of the medulla was collected. 



The study of the tracts and nuclei peculiar to the medulla must 

 be for the present deferred. It is hoped to discuss these points in 

 connection with the study of other, especially lower, Sauropsida. 



6. The minute structure of the nuclei of the cranial nerves. 



(1.) The olfactory h«sbeen already described. 



(2.) The optic fierce tracts may be most conveniently studied in 

 connection with a series of horizontal sections (Plate X.) in con- 

 nection with the transverse. A section through the infundibulum 

 and tuber cinereum at a lower level than the chiasm shows that the 

 oval body protruding from the under surface of the thalamus has 

 a structure similar to that of the tectum of the optic lobes. The 

 epithelium lining the cavity is composed of elongate fusiform cells, 

 which give off processes radiating toward the surface, or, better, 

 their investments are thus produced. It has sometimes seemed to 

 me that these, instead of being mere threads, form a series of more 

 or less completely enclosed columnar compartments, continuous 

 from the ventricle to near the periphery This arrangement is a 

 primitive one, and is quite the rule in the cortex of lower animals, 

 and remains in its primitive form in the retina, tectum opticum, 

 tuber cinereum, and elsewhere in the higher animals. 



At a considerable distance from the ventricle is a mass of gang- 

 lion cells which are arranged in more or less regular concentric 

 rows and also preserve the concentric arrangement. These, for 

 the most part, have well-defined peripheral and basal processes, 

 and are fusiform or pyramidal in shape. Whether these cells are 



