THE SPINAL CORD. 



503 



canal by numerous vascular plexuses, and 

 much loose areolar tissue. The interval 

 between the investing membrane and the 

 sheath of the cord is occupied by a serous 

 membrane (the arachnoid), and the space 

 between the latter membrane and the pia 

 mater is occupied by a fluid called the 

 cerebro-spinal fluid. Within this space 

 the cord is kept in position by proper 

 ligaments, which fix it at different points 

 to its sheath, and by the roots of the 

 spinal nerves, an anterior and a pos- 

 terior root belonging to each, which 

 pass across the space from the surface of 

 the cord towards the intervertebral fora- 

 mina. From its lower part, where they 

 are closely crowded together, the roots 

 of the lumbar and sacral nerves descend 

 nearly vertically to reach the lumbar 

 intervertebral and the sacral foramina, 

 and form a large bundle or lash of 

 nervous cords named the cauda equina, 

 which occupies the vertebral canal below 

 the termination of the cord. 



A Fig. 340. 



-7 C 



10 



Fig. 340. ANTERIOR AND POSTERIOR VIEWS OP 

 THE MEDULLA OBLONGATA AND SPINAL CORD 

 WITH SECTIONS. ^ 



The cord has been divested of its membranes 

 and the roots of the nerves. A, presents an 

 anterior, B, a posterior view, showing the upper 

 or brachial, and the lower or crural enlargements. 

 In these figures the filiform prolongation, repre- 

 sented separately in B', has been removed ; C, 

 shows a transverse section through the middle of 

 the medulla oblongata ; D, a section through the 

 middle of the cervical enlargement of the spinal 

 cord ; E, through the upper region of the dorsal 

 part ; F, through its lower ; Gr, through the 

 middle of the lumbar enlargement ; and H, near 

 the lower end of its tapering extremity. 



1, anterior pyramids ; 1', their decussation ; 

 2, olivary bodies ; 3, restiform bodies ; 4, pos- 

 terior surface of the medulla oblongata ; 4', cala- 

 mus scriptorius ; 5, posterior pyramids ; 6, pos- 

 terior lateral columns passing up into the restiform 

 bodies ; 7, 7, anterior median fissure extending 

 through the whole length of the spinal cord ; 8, 8, 

 anterior lateral groove ; 9, 9, posterior median 

 fissure; 10, 10, posterior lateral groove; x, 

 lower end of the tapering extremity of the cord ; 

 x , x , in B', the filiform prolongation of the 

 cord and its pia-matral covering. 



Although the cord usually ends near the 

 lower border of the body of the first lumbar 

 vertebra, it sometimes terminates a little above 

 or below that point, as opposite to the last 



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