14 Journal of Comparative Neurology. 



viously discussed by Wright and need only be referred to in so 

 far as they affect the dorsal region. Except for the teleostean 

 characteristic of greater concentration of fiber tracts into dis- 

 tinct bundles, the oblongata of Amiiiriis would be directly de- 

 rivable from the ganoid type as presented in Aniia by a concen- 

 tration of structure and a great development of the fasciculus 

 communis system, especially the preauditory portion of its root, 

 and the limitation of the acusticum to the dorsal side. To 

 harmonize the relations here with those in other forms and illus- 

 trate points already made, the following may be noted. 



The enormous enlargement of the dorsal cornua of the myel 

 as the oblongata is approached, is a condition apparently quite 

 universally present in " fishes ;" in Ammrtis the changes closely 

 compare with those in Cyprinoids as described by Mayser. Fig- 

 ures 7-10 will give an idea of how clearly the relation of parts 

 is indicated in Ainiurus. Caudad of the oblongata occurs the 

 enlargement of the dorsal cofrnua ; these, with the surrounding 

 fibers move laterad and the fasciculus communis systems appear 

 on the dorsal portion, the two sides connected caudad of the 

 metatela by the Coinmiss7ira infinia Halleri. The dorsal cornua 

 rapidly diminish and about them on the dorsal and lateral sides 

 the fibers of the spinal Vth tracts appear, — pushed ventrad by 

 the greatly developed fasciculus communis systems (lobi vagi) 

 which now occupy the dorsal region of the oblongata. Cephal- 

 ad of the Xth there appears at the side of the oblongata a new 

 structure, which spreads ventrad covering ectally the spinal Vth 

 tract and soon is capped on the dorsal side by the cerebellar 

 crest. This is easily recognized as the homologue of the acus- 

 ticum of Amia, the tuberciilum acusticum of Wright. In Amitirus 

 and indeed other teleosts, it is not purely dorsal but extends 

 laterally over the oblongata, submerging the spinal Vth which 

 until the appearance of the acusticum, was superficial. The 

 pre- and postauditory portions of the fasciculus communis are 

 differentiated into the so-called "trigeminal" and "vagal" 

 lobes ; the former are enormous and dove-tail into each-other ; 

 they extend dorsad and displace the acusticums laterally (Figs. 

 5 and 11), but no fusion occurs, — at least not in the individuals 



