Method XX 113 



are the greatest and least diameters of the medulla spinalis ? 

 On the basis of function, explain the occurrence of the intumes- 

 centiae (enlargements). 



Carefully remove the radices forming the Cauda equina and, 

 beginning at the intumescentia lumbalis, note the manner in 

 which the medulla spinalis tapers on approaching its termination. 

 Identify the conus meduUaris and the filurh terminale. Make a 

 sketch of the entire medulla spinalis, attaching the names of the 

 various parts. Remove a piece of the filum terminale and tease 

 it under the dissecting lens. Is it nervous ? 



II. SECTIONS OF MEDULLA SPINALIS. 



(a) With a sharp scalpel divide the medulla spinalis at the 

 level of the seventh N. cervicalis, and then remove a thin trans- 

 verse section of the region. Keeping its orientation in mind, 

 place it under the dissecting lens in a watch-glass of water. 

 Note the bilateral symmetry of the section. How is the sub- 

 stantia grisea (gray matter) to be distinguished from the substan- 

 tia alba (white matter) ? What is the general shape of the 

 substantia grisea ? Note differences between dorsal and ventral 

 portions. 



{b) Make a careful sketch of the section, identifying the 

 following structures : 



1. Meninges, etc. — Dura mater spinalis. Arachnoidea spi- 

 nalis. Pia mater spinalis. Septum sub-arachnoidale. Ligamenta 

 denticulata. Arteriae spinales posteriores and anteriores. Venae 

 spinales externae posteriores and anteriores. Sulcus medianus 

 posterior. Septum posterius. Fissura mediana anterior. Septa 

 lateralia. Sulci laterales posterior and anterior. What- is the 

 relation of the latter to the radices posterior and anterior 

 respectively ? 



2. Substantia grisea. — Columna posterior (dorsal horn) with 

 its apex, caput, cervix, and substantia gelatinosa (Rolandi). 

 Formatio reticularis (gray trabeculae). Columna anterior (ven- 

 tral horn), Columna. lateralis (lateral horn). Commissura 

 grisea with its canalis centralis, substantia grisea centralis, its 



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