90 'Journal of Comparative Neurology and Psychology. 



not occur in the selachians, nor do we find there the commissura 

 acustica dorsaHs. The lobi vagales are here much less voluminous 

 than in the codfish and no fusion over the ventricle takes place, 

 which is the explanation also of the fact that in the posterior part 

 of the oblongata the sinus rhomboidalis is so much more spacious. 



Where the medulla oblongata passes into the medulla spinalis 

 and the sinus rhomboidalis closes into the central canal, of course 

 the backward continuations of the acustica and of the communis 

 regions of the two sides finally amalgamate, as shown in Fig. 

 cvii, Plate VII. Here we find a fiber tract connecting both sides, 

 the commissura infima. 



The nucleus Rolandi, which with the surrounding sensory mass 

 causes in Lophius such an important ectal swelling in this place, 

 though not developed in so great measure in Gadus, is, however, 

 in this fish of still greater extent than in the selachians, where it 

 lies dorsally embedded in the spinal cord, as is the case also in 

 reptiles. 



As for the microscopic structure, I can repeat what was already 

 observed when treating of the 'tween-brain, that the strong 

 development of the longitudinal tracts produces so complicated 

 a microscopic aspect in the oblongata that it is a difficult, and in 

 many cases an impossible, task to follow the course of each tract 

 accurately by itself when the investigator does not make use of 

 the embryology or, what is still better, of experimentation after 

 the methods of Gudden, Marchi and Nissl, as Edinger did 

 successfully for some nerve roots. In treating the microscopical 

 structure of the oblongata I shall follow the same order as I did 

 with the teleosts. 



My treatment of the fasciculus longitudinahs lateralis must be 

 very restricted. Already when treating of the mid-brain I ob- 

 served that the frontal end of this tract, which is so strongly 

 developed in Gadus and Lophius, cannot be separated between 

 the great mass of longitudinal fiber-tracts chiefly belonging to the 

 deeper tectum-layer. A slight elevation of the posterior part of 

 the wall under the optic ventricle is present, but diflPerent argu- 

 ments mentioned in the third chapter make it probable that the 

 greater part of the nucleus lateralis mesencephali is embedded 

 in the deep tectum layer, where this layer joins the base of the 

 mid-brain and so the homologue of the fasciculus lateralis of the 

 teleosts runs probably with the tecto-bulbar tract, as it was shown 



