234 C. JUDSON HEREICK 



smaller in Necturus than in most other Amphibia, and for this 

 reason the more fundamental systems of myelinated tracts 

 can be followed here notwithstanding their diffuse formation. 

 On the other hand, the analysis of the much more extensive 

 unmyelinated systems is a problem requiring the most careful 

 study of many different kinds of histological preparations, the 

 silver impregnation methods of Golgi and Ramon y Cajal having 

 been chiefly relied upon in this research. 



With this general orientation in mind, we shall now take up 

 the consideration of the fiber tracts and the functional connec- 

 tions of the parts just enumerated. Notwithstanding the great 

 mass of histological material examined and the variety of tech- 

 nique employed, the results of this study are still very incom- 

 plete and many obscure points remain for future research. 



III. THE PERIPHERAL CONNECTIONS OF THE MIDBRAIN AND 



THALAMUS 



These regions of the brain are connected with the periphery 

 by the III and IV nerves, the mesencephalic root of the V nerve, 

 the nervus terminalis, and the parietal nerve (fig. 65); they are 

 related to the retina through the so-called optic nerve and optic 

 tracts, but since the retina is really a part of the brain these 

 tracts belong morphologically with the lemniscus systems and 

 will be described in the next section. 



The eye-muscle nerves of Necturus have been described by 

 Kingsbury ('95) and by McKibben ('13). The mesencephalic 

 root of the V nerve has been described by Osborn ('88), Kings- 

 bury ('95), Johnston ('05), Norris ('13), and Herrick ('14). 

 Some further details regarding this root in larval Amblystoma 

 are included in my paper on the medulla oblongata of Ambly- 

 stoma ('14 a, p. 361). The central connections of the nervus 

 terminalis of Necturus have been described by McKibben ('11). 

 To these descriptions I have little to add. 



1. The oculoynotor nerve 



The superficial origin of the III nerve lies at the transverse 

 level of the fovea isthmi (p. 221). The heavily myelinated 



