330 



ANATOMY IX A NUTSHELL. 



LESSON XCIV. 



Spinal Cord. (Plates 1V-V-CXCII-CXCIII-CXCIV). 



The spinal cord belongs to the cerebrospinal or central nervous sys- 

 tem, which ('(insists of the brain and spinal cord. The twelve pairs of cranial 

 nerves, and thirty-one pairs of spinal nerves make the peripheral system. 

 Besides these two systems there is the sympathetic system which is connected 

 with these two and closely associated with the vessels, viscera, and glands. 



The spinal cord extends from the level of the foramen magnum (below the 

 decussation of the pyramids of the medulla) to the level of the upper border of 

 the second lumbar vertebra, sometimes only to the first lumbar vertebrae. Its 

 length is from fifteen to eighteen inches and its average weight about one and 

 one-half ounces. It is a somewhat flattened cylinder, wider in the transverse 

 diameter. It follows the curves of the spinal column in which it is lodged. It 

 is composed of white and gray matter, the white on the exterior, and the gray 

 on the interior. The gray matter of the cord consists of two kinds. (1) SUB- 

 STANTIA GELATINOSA (RoLAXDI and CENTRALIS) and (2) SUBSTANTIA SPON- 



GIOSA. Rolandi forms A cap to the posterior horn. It extends the whole 

 length of the cord into the medulla where it becomes enlarged and has large 



PLATE CL. 



SMALL INTESTINE 



Ot'SCENDISG COLON 



ASCENDING COLON 



AORTA 



NFERIOR VENA CAVA 



THEMESSENTERY 



Showing the Peritoneum as a Closed Sac. 



nerve cells and forms one of the end stations for the sensory divisions of the 

 fifth nerve. The substantia gelatinosa Rolandi was formerly thought to be 

 rich in neruoglia tissue, but in fad it is vert poor in this tissue. The cord 

 has two enlargements, i he < i:i;\ ecal ami the lumbar. The former is between 

 the third cervical and the second thoracic vertebra, reaching its greatest diameter, 

 which is transverse, in the sixth cervical, The latter is between the ninth thor- 

 acic and 6rs1 lumbar; its greatesl diameter, which is antero-posterior, is opposite 

 the twelfth thoracic vertebra. These enlargements occur where the nerves are 

 given off to supply the extremities. A- the cord is shorter than the canal, the 

 lumbar, sacral, and coccygeal nerve roots have a longer course than the nerve 



