502 



THE SPINAL COED. 



till at last it is difficult to trace the 

 serial relation of its constituent 

 parts, or any correspondence with 

 the structure of the cord. 



Fig. 339. VIEW OP THE CEREBRO- 



SPINAL AXIS OF THE NERVOUS SYSTEM 



(after Bourgery). -g- 



The right half of the cranium and 

 trunk of the body has been removed by 

 a vertical section ; the membranes of the 

 brain and spinal marrow have also been 

 removed, and the roots and first part of 

 the fifth and ninth cranial, and of all 

 the spinal nerves of the right side, have 

 been dissected out and laid separately on 

 the wall of the skull and on the several 

 vertebrae opposite to the place of their 

 natural exit from the cranio-spinal 

 cavity. 



F, T, 0, lateral surface of the 

 cerebrum ; C, cerebellum ; P, pons 

 Varolii ; m o, medulla oblongata ; m s, 

 upper and lower extremities of the spinal 

 marrow ; c e, on the last lumbar ver- 

 tebra, marks the cauda equina ; v, the 

 three principal branches of the nervus 

 trigeminus or fifth pair ; C I, the sub- 

 occipital or first cervical nerve ; above 

 this is the ninth pair ; C vm, the eighth 

 or lowest cervical nerve ; D I, the first 

 dorsal nerve ; D xii, the last or twelfth ; 

 L i, the first lumbar nerve ; L v, the last 

 or fifth ; S I, the first sacral nerve ; S v, 

 the fifth ; Coi, the coccygeal nerve ; s t 

 the left sacral plexus. 



A. THE SPINAL CORD. 



The spinal cord, or spinal marrow 

 (medulla spinalis), is that part of 

 the cerebro- spinal axis which is 

 situated within the vertebral canal. 

 It extends from the margin of the 

 foramen magimm of the occipital 

 bone to about the lower part of the 

 body of the first lumbar vertebra. 

 It is continued into the medulla 

 oblongata above, and ends below 

 in a slender filament, the filum 

 terminale or central ligament of the 

 spinal cord. 



Invested closely by a proper 

 membrane (the pia mater), the 

 cord is enclosed within a sheath 

 (theca) considerably longer and 

 larger than itself, which is formed 

 by the dura mater, and which is 

 separated from the walls of the 



