304 ELEMENTARY PHYSIOLOGY. [XXIX. 



3. Under a high power repeat the observations 

 of F, Lesson X. and observe further 



a. The outer coat of the pia mater consists 

 chiefly of white fibrous tissue ; the inner 

 chiefly of fine elastic fibrils. 



b. The central canal is lined with a layer of 

 columnar epithelium cells. 



c. In the grey substance, a fine small-meshed 

 network qf fibrils, lying in a punctated or 

 granular-looking matrix. 



d. The nerve fibres, many medullated, of all 

 sizes, throughout the grey substance (in the 

 ring around the central canal the nerve fibres 

 are very few and small, in the substantia 

 gelatinosa they are chiefly the fibres of the 

 posterior roots). Note the fibres running 

 across the anterior and posterior grey com- 

 missures and compare the anterior grey with 

 the white commissure. 



4. Prepare transverse sections of the spinal cord of 

 a cat or dog taken through the dorsal and lum- 

 bar regions (say through origin of 9th dorsal and 

 4th lumbar nerves) and compare them with the 

 section of the cervical region. Observe 



a. The sections taken from the cervical and 

 lumbar regions are larger than those taken 

 from the dorsal region. 



b. The enlargements in these regions are largely 

 due to an increase in the quantity of grey 



