EXPLAKATIOI OF THE PLATES. 



Plates I-IX are sections from the medulla, magnified about 7 diam(?ters, as seen with a three 

 inch objective. 



PLATE I. 



Fig. 1. Section of the medulla of the sheep, just above the spinal cord, showing the partial decus- 

 sation of the pyramids from which the raphe is already formed, and the first appearance of the hypo- 

 glossal roots. 



Fig. 2. Transverse section from the same, a little higher up, showing the formation of the olivary 

 bodies, the hypoglossal roots, the restiform and post-pyramidal nuclei. 



Fig. 3. Transverse section from the same medulla, showing the enlargement of the central canal, 

 and the complete formation of the hypoglossal and vagal nuclei. 



Fig. 4. Transverse section from the same, still higher, showing the opening of the central canal 

 into the fourth ventricle which is now completely formed, and on each side of which are seen the 

 vagal and hypoglossal nuclei. 



PLATE II. 



Fig. 5. Transverse section from the medulla of the sheep, showing the central portion on each side 

 of the raphe. In front are seen the narrow pyramids and behind the olivary bodies ; posteriorly on 

 the floor of the ventricle lie the hypoglossal and vagal nuclei. The course of the hypoglossal roots 

 is very plainly seen. 



Fig. 6. Transverse section at about the same height, showing the same nuclei with their roots, 

 and the commencement of the auditory nucleus. 



Fig. "T. Transverse section, a little higher up ; the hypoglossal roots are now no longer visible ; 

 the vagus nucleus has reached its maximum development and is already pushed forward by the forma- 

 tion of the auditory nucleus which has attained considerable size. The vagus roots are very distinctly 

 seen, forming several quite large bundles which traverse the caput cornu. 



Fig. 8. Section from the same medulla, still higher, showing the development and formation of the 

 anterior and posterior portions of the auditory nucleus, with the posterior auditory roots. 



PLATE III. 



Fig. 9. Section from the medulla of the sheep, showing the auditory nucleus and roots together 

 with their connections with lobes of the cerebellum. 



Fig. 10. Transverse section from the same medulla, showing the further development of the audi- 

 tory nucleus and anterior root of the auditory, together with the facial nucleus and root. The fibres 

 from the anterior auditory root which penetrate the restiform body, joining the posterior root of the 

 auditory, are especially well shown in this figure. 



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