352 C. JUDSON HERKICK 



lateral recesses, whose walls form the auricular lobes of the 

 medulla oblongata. 



In the flat and wide medulla oblongata of Necturus I have 

 described ('14, figs. 1, 2, 3, 15, 16) in the floor of the fourth 

 ventricle a sulcus limitans separating the motor and sensory 

 columns, and farther laterally a sulcus lateralis which forms the 

 medial boundary of the area acustico-lateralis. In larval Ambly- 

 stoma these sulci are in some places obscurely evident, but on 

 account of the narrower and higher form of the oblongata in these 

 larvae they are not so simply related to the underlying regions, and 

 in the adult the deviation from the form seen in Necturus is still 

 greater. 



In the caudal part of the fourth ventricle there is a shallow 

 sulcus limitans (fig. 2, s.L), which separates the ventral motor 

 lamina from the dorsal sensory lamina; and in the sensory lamina 

 there is an obscure visceral lobe (fig. 2, lob.vis.) formed by the 

 fasciculus solitarius and its associated gray matter (figs. 14 to 

 17), which clearly corresponds with the so-called lobus vagi of 

 fishes. Near the lower end of the fourth ventricle this visceral 

 lobe arises up behind the caudal end of the area acustico-lateralis 

 almost to the dorsal border of the rhomboidal lip (figs. 2, 17). 



In the rostral half of the oblongata the massive wall on each 

 side consists of a horizontal lamina which coincides approximately 

 with the motor region, and a vertical lamina which is composed 

 chiefly of the area acustico-lateralis, but the sulcus separating 

 these two laminae does not coincide exactly with the embryonic 

 sulcus limitans. The motor VII nucleus, like the nucleus am- 

 biguus, lies far medial, but the motor V nucleus (fig. 1, nuc.V.m.) 

 has been crowded lateralward by the great subcerebellar tegmen- 

 tal eminence (fig. 2, em.s.t.) and is in part overlapped by the great 

 sensory trigeminal nucleus which forms the greater part of the 

 eminentia trigemini (fig. 9) . 



The area acustico-lateralis forms the rhomboidal lip for nearly 

 the entire length of the oblongata, from the tip of the auricular 

 lobe almost to the calamus scriptorius. It is defined as the area 

 which receives root fibers of the VIII and lateral line nerves and 

 its extent may be seen at a glance in figure 3. As in Necturus, it 



