The Nervous System 2 1 9 



white matter is within, and the gray matter is on the 

 surface. In the cord the gray matter is arranged in two 

 half-moon-shaped masses, the backs of which are connected 

 at the central part. The white matter, consisting mainly 

 of fibers, running for the most part in the direction of the 

 length of the cord, is outside of and surrounds the gray 

 crescents. 



Thus each half or side of the cord has its own gray 

 crescent, the horns of which point one forwards and the 

 other backwards, called respectively the anterior and posterior 

 cornua, or horns. 



It will also be seen that the white substance itself, in 

 each half of the cord, is divided by the horns of the gray 

 matter and by fibers passing from them into three parts, 

 which are known as the anterior, posterior, and lateral 

 columns (Fig. 120). 



Experiment 96. Procure at the market an uninjured piece of the 

 spinal cord from the loin of mutton or the sirloin or the rib of beef. 

 After noting its general character while fresh, preserve it in one of 

 the fluids just mentioned (note, p. 216), until it is sufficiently hard to 

 be cut in sections. 



335. The Spinal Nerves. From the gray matter on each 

 side of the spinal cord thirty-one spinal nerves are given off 

 and distributed chiefly to the muscles and the skin. They 

 pass out at regular intervals on each side of the canal, by 

 small openings between the vertebrae. 



Each spinal nerve has two roots, one from the anterior, 

 the other from the posterior, portion of the cord. These 

 unite and run side by side, forming as they pass between 

 the vertebrae one silvery thread, or nerve trunk. Although 

 bound up in one bundle, the nerve fibers of the two roots 

 remain quite distinct and perform two entirely different 

 functions. 



