MEDULLA OBLONGATA OF AMBLYSTOMA 345 



material permits. A wax model was constructed from the older 

 of these specimens (figs. 1, 2, 3). The sections from which this 

 model was constructed are 15/i in thickness and the scales at- 

 tached to the figures give the serial numbers of the sections. 

 Fifteen of these sections are illustrated in figures 4 to 18. In the 

 descriptions of these sections their respective serial numbers are 

 stated, so that reference to the scales attached to figm*es 1 to 3 will 

 permit a ready locaHzation of each section in its place in the 

 model. 



The fiber tracts of the 17 mm. specimen (23 days old) are not as 

 fully developed as in the older one modeled, but so far as revealed 

 they exhibit the same arrangement. Longitudinal sections of 

 several Amblystoma lavae from 20 mm. to 60 mm. long prepared 

 by Ram6n y Cajal's method were also studied for additional 

 control and various cytological methods were also used. Weigert 

 preparations of a second specimen of 23 days shows that at this 

 age few myelinated fibers are present in the oblongata, though 

 some very coarse ones are found in the fasciculus longitudinally 

 medialis. I have studied an extensive series of Golgi preparations' 

 of larval and adult Amblystoma, comprising more than 150 speci- 

 mens. The methods of Weigert and Ramon y Cajal have also 

 been applied to the adult brain. The adult has not been studied 

 as exhaustively as the larva, but so far as observed the adult in 

 all fundamental relations resembles the larva. 



In this study the sensory centers and theu' connecting tracts 

 have been most carefully examined, though the motor apparatus 

 has also received attention. The analysis even of the sensory 

 apparatus is far from complete, but it is adequate to show the 

 general arrangement and most important connections. This 

 arrangement is simple and probabh^ very primitive and it is 

 hoped that this analysis may serve as a point of departure for 

 studies in the evolution of the medulla oblongata of vertebrates. 



Here, as in general throughout the urodele brain, there are few 

 clearly differentiated gray centers, but the cell bodies of all the 

 neurones retain their primitive positions in the central gray 

 (stratum griseum), while all fiber tracts and synapses are found 

 in the superficial stratum album. Occasional nuclei are found in 



