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EXPLANATION OF PLATES. 

 PLATE IV. 



Fig. I. Frontal section through the rhomboidal fossa of the brain of an 

 embryo rat (Mus decumanus, var. alba) three millimeters long N. B., near the 

 region of the X nerve, x 60. The section is slightly oblique. 



Figs. 2, J and ^. Frontal sections of a human embryo forty-two millimeters 

 long. The head had previously been partially sectioned sagittally. x 6. 



Fig. J. Sagittal section of the same embryo near the meson, x 9. 



Fig. 6. Sagittal section near the meson of a human embryo twenty two 

 millimeters long, x 10. 



Figs. 7 and 8. Frontal sections of the same embryo. Fig. 7 caudad of the 

 X, Fig. 8 at the X nerve, xii. 



PLATE V. 



Fig. p. Frontal section of an embryo cat ten millimeters long N. B. 

 through the ganglion of the X nerve, x 22. 



Fig. 10. Amplification of the region marked Sec. rhomboidal lip in Fig, 

 9. X 450. 



