148 Cincinnati Society of Natural History. 



the middle and posterior brain vesicles." Josef Bellonci, " Ueber 

 die centrale Endigung des nerviis opticus bei vertebraten," Zeits. 

 Wiss. Zool., Bd. XLVIL, p. 37. 



In sections somewhat nearer the median line are the apparent 

 homologues of the corpora geniculata thalami (Plate IX, Fig. 9, 

 c.gn.) In more lateral sections the division of the optic tract into 

 fascicles which pass to the anterior, lateral and posterior surface of 

 the tectum opticum are shown, while other minor bundles seem to 

 pass back of or through the corpora geniculata. No fibres of the 

 optic tract reach any other locus than the tectum directly, so far as 

 observed. The greatest obscurity still prevails as to the structure 

 and function of the tectum opticum. There remains no doubt 

 that much the greater part of the fibres from the optic tracts end in 

 the tract constituting the superior layer of the tectum, but in spite 

 of almost perfect sections through this region in several directions, 

 the essential structure remains obscure. It seems exceedingly 

 probable that the function is that of internal analysis, somehow 

 corresponding to the external analysis in the retina, to which its 

 structure is very similar. The columnar compartments set off by 

 pillars of connective tissue and containing oval or globular cells, 

 resemble the retinal structure obviously. Plate XII., Figs. 8, 9. 

 indicate the most important relationships. The nervous elements 

 can scarcely be distinguished from the connective. Among the 

 latter are fusiform deeply staining cells, which have been described 

 as the true nervous elements of the tectum, but which are almost 

 certainly the inoblasts of the connective pillars of the tectum. 



On the ventricle side these pillars arise from the intervals 

 between the large epithelium cells, and continue without inter- 

 ruption to the outer surface, even intersecting the superficial tract. 

 Near the ventricle are several concentric rows of flask-cells mingled 

 with Deiter's corpuscles. Near the median line these concentric 

 rows fuse and are associated with enormous cells, much larger 

 than any elsewhere in the brain, and more nearly resembling the 

 Perkinje's cells of the cerebellum than any other type. These cells 

 have their processes directed peripherally. In the columnar com- 

 partments above mentioned, there are many Deiter's corpuscles as 

 well as the oval or flask-cells described. It is uncertain whether the 

 pyramidal or irregular multipolar cells among the others are really 

 nervous, and if so, whether they are related to those previously 

 described or not. The central fibres collect in a tract near the 



