198 NERVOUS SYSTEM OF VERTEBRATES. 



DEMONSTRATION OR LABORATORY WORK. 



1. Review the dissections of spinal and cranial nerves already 

 made, with especial reference to the position of the ventral roots and 

 the relation of the rami to the muscle segments. Dissect the brachial 

 and cervical plexuses of a selachian. 



2. Examine carefully the somatic motor cranial nerves, noting their 

 segmental arrangement with reference to the dorsal roots and the num- 

 ber and position of the "hypoglossal roots" present. Selachian brains 

 are especially useful for this. Small roots which would ordinarily be 

 overlooked can be brought sharply to view by painting the dissection 

 with a one percent, solution of osmic acid which is well washed away 

 with water as soon as the nerves are blackened. 



3. In sections by the Weigert or Golgi method study the somatic 

 motor nuclei and the formation of the ventral roots. Selachian or 

 frog. 



4. Upon the basis of the descriptions given in previous chapters 

 construct diagrams representing the course of impulses the centers 

 and tracts involved in somatic motor reflexes aroused by cutaneous, 

 auditory, optic and olfactory stimuli. 



LITERATURE. 



Bardeen, C. R. : The Bimeric Distribution of the Spinal Nerves in Elas- 

 mobranchii and Urodela. Amer. Jour, of Anat., Vol. 3. 1904. 



Fiirbringer, M.: Ueber die spino-occipitalen Nerven der Selachieru. s. w. 

 Gegenbaur's Festschrift, Bd. 3. 1897. 



Johnston, J. B.: The Cranial Nerve Components of Petromyzon. Morph. 

 Jahrb., Bd. 34. 1905. 



Koltzoff, N. K.: Entwickelungsgeschichte des Kopfes von Petromyzon 

 planeri. Bull. Soc. Imper. d. Natural, de Moscou, Annee 1901, No. 3-4. 1902. 



Neal, H. V.: The Development of the Hypoglossus Musculature in 

 Petromyzon and Squalus. Anat. Anz., Bd. 13. 1897. 



Neal, H. V.: The Development of the Ventral Nerves in Selachii. i. 

 The Spinal Nerves. Mark Anniversary Volume. 1903. 



van Wijhe, J. W.: Ueber die Mesodermsegmente und die Entwickelung 

 der Nerven des Selachierkopfes. Amsterdam 1882. 



Worthington, Julia: The Descriptive Anatomy of the Brain and Cranial 

 Nerves of Bdellostoma Dombeyi. Quart. Jour. Mic. Sci., Vol. 49. 1905. 



