ME. J. L. CLAEKE ON THE GEET SUBSTANCE OE THE SPINAL COED. 467 
near the middle of the dorsal region, magnified 220 diameters : — c, the inner 
portion, adjoining the grey substance between the anterior and posterior 
cornua (see fig. 6, F, Plate XXI.); b, the free extremity extending trans- 
versely across the lateral column ; a, a, a, fasciculi of longitudinal fibres of the 
lateral column. The tractus is interspersed with cells, from some of which 
the processes escape with nerve-fibres into the lateral column ; while others 
are continuous with nerve-fibres proceeding from the transverse commissure 
and other deep parts of the grey substance. At its inner end {c), some of the 
cells with their processes are elongated towards the anterior and posterior 
cornua (compare fig. 6, Plate XXI.). 
Fig. 52, Plate XXII. Cells from a transverse section of the tractus intermedio-lateralis of 
the Ox, magnified 220 diameters. 
Fig. 53, Plate XXII. Epithelial-cells from the spinal canal of the Ox, magnified 400 
diameters : — a, isolated cells (the letter is placed over their free, ciliated 
end); b, same cells packed together in situ, and bearing cilia, which project 
into the canal. 
Fig. 54, Plate XXII. Epithelium from the spinal canal of the Tortoise : — a, b, separate 
cells, magnified 400 diameters ; G, part of spinal canal, with the cells dis- 
posed around it, and a little less magnified ; c, free nuclei from the white 
columns: magnified 400 diameters. 
Fig. 55, Plate XXII. Human spinal canal from the cervical region. Its outer parts are 
filled up with a heap of epithelial-nuclei, in the midst of which are two 
secondary canals, surrounded by the usual regular layer. 
Fig. 56, Plate XXII. Longitudinal section of part of the tractus intermedio-lateralis, 
magnified about 200 diameters. The cells are elongated longitudinally at the 
verge of the lateral column, the fibres of which are accompanied by their 
processes. 
