88 BULLETIN OF THE LABORATORIES 



PLATE XI. 



C. L. Herrick. 



The figures of this plate are chiefly intended to facilitate a comparison of 

 the brain of Arctomys with other animals. 



F/o-. I. Median longitudinal section of the brain of a young raccoon, Pro- 

 cyan lotor. The interrupted character of the calloso-marginal convolution along 

 its margin and the highly convoluted limbic region are noteworthy. The prim- 

 itive condition seen in the lack of a curvature in the brain axis is more than com- 

 pensated for by the backward projection of the cerebrum, nearly covering the 

 comi)act and closely convoluted cerebellum. The relations of the scarcely arched 

 corpus callosum, fornix, anterior commissure, thalamus, pineal body, and mesen- 

 cephalon, are well shown in the figure. 



Fig. 2. Dorsal surface of a raccoon of the same age. The figures indicate 

 positions stimulated by the electric current as described in the text. 



■^^S"- 3- Ventral surface of another specimen of the same age, somewhat 

 shorter than when in natural relations. The peculiar relations of the olfactory 

 and optic tracts are noteworthy. The mammillary bodies and the plainly indi- 

 cated tracts of the medulla may also be noted. The position of the third, fifth, 

 seventh, and eighth roots alone is indicated. 



Ffg. 4. Dorsal surface of cerebrum of adult raccoon, somewhat shrunken 

 and distorted. 



Fig. 5. Dorsal surface of cerebrum of a quarter grown pup. x, indicates 

 a lesion resulting in slight motor disturbance of the hind leg of the opposite 

 side. 



Fig. 6. Ventral surface of the brain of a kitten. With eyes still closed. 



Fig, 7. Dorsal view of the same brain. 



Figs. 8-1 1. Transverse sections of the cerebrum of the raccoon. Fig. 9, 

 22 mm. back of anterior margin. Fig. 10, 36 mm. back of anterior margin and 

 just back of the chiasm. 



Fig. II. Still near the posterior or occipital margin of the hemispheres. 



Fi£s. 12-I4. Sections of the brain of the rabbit, Leptts sylvaticns. Fig. 12. 

 View of corpora quadrigemina and left hemisphere from behind. 



Fig. 13. Section at the middle region, and 



Fig. 14. Near the anterior of the hemispheres. 



Figs. 15-17, Cellular structure of the brain of the oppossum, Didelphys, 

 Fig. 15. Portion of the cortex in front of crucial sulcus near the median line. 

 Fig. 16. Cells from the hippocampal region. Fig. 17. An instance of anasta- 

 mosis of CO ordinate motor pyramids. 



Figs. 8 19. Ventral and lateral views of brain of adult opossum. 



Fig. 20. Transverse section of same brain at anterior commissure. 



PLATE XIL 



C. L. Herrick. 

 Fig, I. Horizontal section of left hemisphere and thalamus behind the corpug 



