THE CENTRAL NERVE SYSTEM 349 



gray matter is expanded into a projection called the 

 lateral horn. This is seen on both sides. Microscopic 

 examination of the gray substance will show that it 

 is practically an aggregation of neurones nerve cells 

 with their dendrites and non-medullated axones, 

 lymphatics, bloodvessels, all supported in a frame- 

 work of non-neural tissue the neuroglia. 



Classification of nerve cells within the gray sub- 

 stance as regards their function: They are divided 

 into intrinsic, efferent, and afferent. 



The intrinsic cells are simply associative or connec- 

 tive in character, their processes enteV the white 

 substance horizontally, and give off branches which 

 ascend -and descend, reen'tering the gray substance 

 at different levels, where their axones again associate 

 with the dendrites of other intrinsic cells. 



The efferent motor cells is the term given to the 

 cells found in the anterior horns, whicn are sub- 

 stations for the reception from the brain and other 

 neurones, of motor impulses which they in turn 

 conduct through their efferent axones, to the periphery, 

 and promote activity in the muscles, glands, viscera, 

 bloodvessels, as well as influence the growth, develop- 

 ment, and metabolism (trophic) of the tissues. 



Afferent cells (sensor) is the name given to the 

 cells of the posterior horn, which receive from the 

 afferent nerves impulses and conduct the same by 

 their afferent axones, to the cortex of the brain, giving 

 rise to conscious sensations, as heat, pain, sensation 

 of touch, etc. 



The Spinal Nerves. There are thirty -one pairs, 

 divided according to the portion of the cord they 

 arise from, as follows: 



Cervical pairs 8 



Thoracic pairs ,. 



Lumbar pairs . - v A a^- 



Sacral pairs . . . _ . "" 



Coccygeal pairs 



Total 



; 1* 



