THE SPINAL CORD. 395 



matter is enclosed within the white, and exists in the shape 

 of two large " commas " ('), turned with the head anterior, 

 the convex surfaces turned toward each other, and con- 

 nected at their middle by the gray commissure. 



Here we must pause. The subject of the internal arrange- 

 ment of the cord and brain is most fascinating, but it does 

 not properly enter into the scope of such a manual of 

 anatomy as this. However, the student should not be con- 

 tent to let the matter rest here, but should pass from this 

 hasty and necessarily incomplete description of the brain 

 and cord to the microscopic anatomy of the same, then to 

 their functions, and lastly to the application of all this 

 knowledge to the workings of medical and surgical practice. 



The Spinal Nerves. Fig. 8 1 . 



They arise from the side of the cord in 32 pairs by two 

 sets of roots as already indicated, the anterior (motor) 

 and posterior (sensory), the former being smaller than 

 the latter. Inasmuch as the spinal cord does not reach 

 to the lower extremity of the spinal canal, it follows that, as 

 the spinal nerves leave the cord they have to descend in 

 order to leave by their proper foramen, the downward 

 inclination of the nerves increases from above downward, 

 until at the lower end of the cord the canal is filled with the 

 nerves from below the last dorsal vertebra, which run 

 parallel with each other and then slightly outward to reach 

 their foramen of exit ; this arrangement produces a tasseled 

 appearance named the cauda equina. 



The point at which the spinal nerves leave the side of 

 the cord and their points of emergence are given in the 

 following table copied from Gowers : 



