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ANATOMY AND PHYSIOLOGY 



impressions from the various parts of the body to the centers which 

 receive them. We commonly speak of motor nerves as running 

 down, and sensory nerves as running up, referring them to the 

 spinal cord or brain. 



THE SPINAL CORD 



The spinal cord lies within the spinal canal in the spinal 

 column, being continuous with the brain. It is a round white 

 structure about seventeen inches long, ex- 

 tending from the atlas to the second lum- 

 bar vertebra, where it ends in a slender ter- 

 minal filament which continues to the end 

 of the canal. The thickness is about half 

 an inch, being greater in the lower cervical 

 and lower dorsal regions, making the cervical 

 and lumbar enlargements where nerves are 

 given off for the extremities. It presents 

 a median fissure in front and another at the 

 back, marking off its right and left halves. 

 Other fissures divide each half into anterior, 

 lateral, and posterior columns or tracts. 



A transverse section will show that the 

 interior of the cord is grayish in color in- 

 stead of white, and this portion is largely 

 made up of the gray cell bodies and their 

 branches, arranged in masses which are con- 

 tinuous throughout the length of the cord. 



The section will also show that the area 

 occupied by the gray portion roughly re- 

 sembles two crescents (one in either side), 

 connected together across the middle. The 

 extremities of the crescents are called the 

 anterior and posterior horns. 



A canal, called the central canal, runs 

 through the center of the gray portion. It 

 may be traced throughout the length of the cord but is easily seen 

 only in the upper part. It contains cerebrospinal fluid. 



The white portion consists of the bundles or tracts of the cord 

 (often called columns, the name tract being applied to divisions of 



FIG. 174. THE BRAIN 

 AND SPINAL CORD. 

 (Quain, after Bourgery.) 



