Herrick, Commissura Infima. 421 



The somatic sensory centers of the spinal cord have shown no 

 tendency to migrate into the head, Hke that seen in the visceral 

 sensory centers. Even in Prionotus, where the most cephahc seg- 

 ments of the spinal cord alone are greatly enlarged, there is no 

 especial tendency for them to be concentrated in the medulla 

 oblongata. In the oblongata, however, the somatic sensory 

 centers have always suffered extreme modification. The somatic 

 sensory zone in the cephalic end of the oblongata has given rise 

 to the tuberculum acusticum and cerebellum and because of the 

 crowding due to the presence of these structures, or for some other 

 reason, in teleosts practically all of the tactile, or unspecialized 

 somatic sensory nerves from the skin of the head pass back in the 

 spinal V tract to terminate in the funicular nucleus region. In 

 some fishes there is a separate and well defined spinal V nucleus; 

 in others this is indistinguishable from the dorsal cornu and funicu- 

 lar nucleus. The latter is a derivative of the formatio reticularis, 

 which also gives rise to the somatic commissural nucleus. The 

 somatic commissura infima is a continuation of the commissure 

 of the dorsal cornua and fascicuh proprii of the spinal cord. It 

 receives also large additions from the funicular and spinal V 

 nuclei. The commissure of the tubercula acustica in fishes hke 

 Gadus and Haploidonotus, where these fuse above the ventricle, 

 is probably homologous, and also a part of the commissural fibers 

 of the cerebellum. 



LITERATURE CITED. 



Cajal, S. R. y. 



1896. Beitrag zum Studium der Medulla oblongata, des Kleinhirns und der Ursprungs der 

 Gehirnnerven. Trans, by Bresler. Leipzig. 

 Herrick, C. Judson. 



1905. The central gustatory paths in the brains of bony fishes. Journ. Comp. Neur. and 



Psychol., vol. 15. 



1906. On the centers for taste and touch in the medulla oblongata of fishes. Ihid., vol. i6. 



1907. A study of the vagal lobes and funicular nuclei of the brain of the codfish. Ihid., 



vol. 17. 

 1907a. The tactile centers in the spinal cord and brain of the sea robin (Prionotus carolinus L) 

 Ihid., vol. 17. 

 Kappers, C. U. a. 



1906. The structure of the teleostean and selachian braiii. Journ. Comp. Neur. and Psychol., 



vol. 16. 



1907. Untersuchungen iiber das Gehrin der Ganoiden Amia calva und Lepidosteus osseus. 



Ahhandl. Senckenhergischen Naturf. Gessellschafl, Frankjurt,'RA. ^o, Heft 3, 1907. 



