2l6 NERVOUS SYSTEM OF VERTEBRATES. 



toward their innervation territory, from the spinal ganglia into 

 the viscera, but it is just these sensory cells whose existence and 

 arrangement are in dispute. The excitatory neurones in the 

 sympathetic system belong to a special category. They seem to 

 have had their origin from neural crest material, but whether as 

 modified spinal ganglion cells or directly from indifferent ecto- 

 dermal cells there is no evidence. The double origin of the ciliary 

 ganglion in the chick is of interest in this connection. 



Regardless of these unsettled theoretical questions it should be 

 held clearly in mind that the sympathetic system is an offshoot 

 or subsidiary portion of the visceral afferent and efferent divisions 

 of the nervous system which has come to have a special structure 

 and arrangement owing to the conditions of visceral activities. 



DEMONSTRATION OR LABORATORY WORK. 



1. Dissect the sympathetic system of a frog and a mammal. 



2. Study sections of sympathetic ganglia prepared by the Golgi or 

 methylene blue method. 



LITERATURE. 



Balfour, F. M.: Monograph on the Development of Elasmobranch Fishes. 

 1878. 



Balfour, F. M.: Comparative Embryology. Vol. 2. 1885. 



Cajal, S. R. : Textura del sistema nervioso del Hombre y de los Vertebrados. 

 Tomo II, segunda parte. 



Dogiel, A. S.: Zur Frage iiber den feineren Bau des sympathischen Nerven- 

 systems bei den Saugethieren. Arch.f.mik.Anat., Bd. 46. 1895. 



Gaskell, W. H.: On the Structure, Distribution and Function of the Nerves 

 which innervate the Visceral and Vascular Systems. Jour, of Physiol., Vol. 

 7. 1886. 



Van Gehuchten, A. : Les cellules nerveuses du sympathique. La Cellule, 

 Tome 8. 1892. 



Herrick, C. Judson: The Cranial Nerves of Menidia. Jour. Comp. Neur., 

 Vol. 9. 1899. 



His, W., jr.: Die Entwickelung des Herznervensystems bei Wirbelthieren. 

 Abhdl. Math.-physischen Classe d. Konigl. Sachsischen Gesell.d.Wiss., Bd. 8. 

 Leipzig. 1891. 



Hoffmann, C. K.: Zur Entwickelungsgeschichte des Sympathicus. i. Die 

 Entwickelung des Sympathicus bei den Selachiern (Acanthias vulgaris). 

 Verhandl. K. Acad. Wetensch. Amsterdam. 1900. 2. Die Entwickelungsge- 

 schichte des Sympathicus bei den Urodelen. Ibid. 1902. 



