THE SI'IXAL CORD 



TJI 



the encephalon. After birth it grows more rapidly and for a longer period than the 

 enccplialon, increasing in weight more than sevenfold, while the brain increases less 

 than half that amount. Its specific gravity is given as ro.'iv 



The line of division between the spinal cord and the medulla oblongata is arbi- 

 trary. The outer border of the foramen magnum is commonly given, or, better, a 

 transverse line just below the decussat ion of the pyramids. Lying in the vertebral 

 canal, the adult cord usually extends to the upper border of the body of the second 

 lumbar vertebra. However, cases may be found in which it extends no farther than 

 the last thoracic vertebra. Up to the third month of intra-uterine life it occupies 



FIG. 564. DIAGRAM ILLUSTRATING THE GROSS DIVISIONS OF THE CENTRAL NERVOUS SYSTEM. 



PKOSBXI'KPn- 

 ALOX (fort- 

 train) 



OLIVARY BODY la 



MESEXCKPHALOS (mid 

 brain} 



. CERRBKL- 

 Ll'M 



(hind-brain) 



KlIOMBKX- 

 CKPUALOX 



KXCKPHALOS 



(train) 



- PASS IBR r 1C A 1.1 3 



~~PAKS THORACALIS 



PARS Ll'MBALIS 



PARK SACKAllS OK 

 XHVI'LLARIS 



fl-IXAI. CORD 

 tmeduUa tpinalit) 



the entire length of the vertebral canal, but owing to the fact that the vertebral 

 column lengthens more rapidly and for a longer period than does the spinal cord, the 

 latter, being attached to (lie brain above, soon ceases to occupy the entire canal. 

 At birth its average extent is to the body of the third lumbar vertebra. 



External morphology. In position in the body, the spinal cord conforms 

 to the curvatures of the canal in which it lies. In addition to the bony wall 

 of the vertebral canal, it is enveloped and protected by its three membranes or men- 

 inges, which are continuous with the like membranes of the encephalon: first, the 

 pia mater, which closely invests the cord and sends ingrowths into its substance, 



