110 PROCEEDINGS OF THE AMERICAN ACADEMY 



in length, magnified 145 diameters. G', intercolumnar mass of gray substance, 

 the beginning of Goll's Keilsiriinge. B', thickening of tlie posterior columns, tlie 

 beginning of Burdach's Keilstrange. 



Fig. 3. A cross section through tlie lumbar region of the same embryo, mag- 

 nified 410 diameters. 



Fig. 4. A cross section through the lumbar enlargement of the same embryo, 

 magnified 410 diameters. 



Fig. 5. A cross section through the lumbar enlargement of an embryo 60 

 mm. in length, magnified 410 diameters. 



Fig. 6. A cross section through the lumbar enlargement of an embryo 100 

 mm. in length, magnified 145 diameters. 



Fig. 7. A cross section through the lateral column and adjacent gray sub- 

 stance of an embryo 60 mm. in length, magnified 410 diameters. 



Fig. 8. A cross section through tlie lumbar region of an embryo 97 mm. in 

 length, magnified 145 diameters. 



Fig. 9. A cross section through the cervical region of an embrj'o 145 mm. in 

 length, magnified 145 diameters. 



Fig. 10. A cross section from the lumbar region of an embryo 75 mm. in 

 length, showing the elongation of the epithelial cells in the dorsal wall of the 

 canal into fibres, magnified 470 diameters. 



Fig. 11. A cross section through the cervical region of an embryo 85 mm. in 

 length, magnified 410 diameters. 



Fig. 12. A cross section through the dorsal region of an embryo 47 mm. in 

 length, magnified 410 diameters, showing the disposition of the fibres and nuclei 

 at the anterior wall of the central canal. 



Cambridge, June, 1883. 



