182 



Nachdruck verboten. 



A Comment upon recent Contributions on the Brain 

 of Petromyzonts. 



By J. B. Johnston, University of Minnesota, U. S. A. 



With 9 Figures. 



(Schluß.) 



Upon entering the brain these visceral sensory fibers turn caudad 

 near the ventricular surface, forming thus a longitudinal 

 bundle known in lower vertebrates as the fasciculus communis and in 

 man as the fasciculus solitarius. This fasciculus is always clearly se- 

 parate and distinct from the somatic sensory fibers (Nn. acusticus, la- 

 teralis and trigeminus). The visceral sensory fibers are usually more 

 slender than the somatic sensory fibers and a dichotomous division of 

 the visceral sensory fibers is rare or inconspicuous. The fasciculus 

 solitarius (communis) is always accompanied by a column of gray 

 matter into which the fibers send their end branches. This column 

 of gray matter lies next dorso- lateral to the sulcus limitans of His. 

 It constitutes the more ventral of the two sensory columns while the 

 acustico-lateralis centers and the substantia gelatinosa trigemini con- 

 stitute the more dorsal sensory column in the myelencephalon. The 

 more ventral of the two columns has been known by the names: lobus 

 vagi, lobus facialis et vagalis, lobus visceralis and gray matter of the 

 fasciculus solitarius. It may best be called the visceral sensory column. 

 This column, at the calamus scriptorius rises to the dorsal surface of 

 the brain medial to the somatic sensory column, and meets its fellow 

 in a median nucleus, the nucleus commissuralis, through which the 

 fibers of the tractus solitarius form a decussation. 



According to Tretjakoff (p. 659) the sensory fibers of the N. 

 glossopharyngeus and part of those of the N. vagus when they enter 

 the brain run in the tractus spinalis trigemini and the rest of the 

 sensory fibers of the N. vagus "verlaufen im Gehirn über den Tr, sp. 

 trig," All these fibers divide dichotomously and form ascending 

 and descending branches as do the root fibers of the N. acusticus or 

 lateralis. "Der dorsale Rand des Rückenmarkes von Ammocoetes", 

 says the author, "wird eigentlich mit Unrecht als Lobus vagi be- 

 zeichnet, wie er häufig genannt worden ist. Die Fasern des Nervus 



