BOOK IX. 



PART II. 



On the Special Anatomy of the Central portion of the Nervous System. 



CHAPTER I. 



OF THE SPINAL MARROW AND ITS MEMBRANES. 



THE Spinal Marrow, (Medulla Spinalis) though commonly 

 described after the brain, as a continuation or appendage of it, 

 has precedence, as seen, both in the period of its formation in 

 the embryo, and in its importance to the functions of the ani- 

 mal system; it will, consequently, be proper to give it that prio- 

 rity in description to which its natural rank entitles it. 



SECT. I. OF THE SPINAL MARROW. 



It is placed within the vertebral cavity, and extends from the 

 first vertebra of the neck to the first or second vertebra of the 

 loins, inclusively. It is surrounded by three membranes, of 

 which the Dura Mater is external, the Pia Mater internal, and 

 the Tunica Arachnoidea, between the other two. Its general 

 form is cylindrical, yet it has slightly the appearance of being 

 flattened both behind and before. It departs also from the strict 

 cylindrical shape, by being enlarged or swollen at particular 

 points. One of these enlargements occurs in the neck, where 

 the spinal canal is formed by the five lower cervical vertebrae, 

 and the roots of the axillary plexus of nerves are given off. The 



