MEDULLA SPINALIS.— LIGAMENTUM DENTICULATUM. 395 



large and broad; those of the back are slender: and those of 

 the loins, and upper part of the sacrum, are very large. 



The uppermost of the fasciculi of the spine proceed almost at 

 right-angles with the medulla spinalis, to the foramina through 

 which they pass : those which are lower pass off in a direction 

 obliquely downwards ; and the lowermost are almost perpen- 

 dicular. Between the anterior and posterior fasciculi, a fine 

 ligamentous chord passes, which is attached above to the dura 

 mater as it passes through the foramen magnum, and continues 

 to the OS coccygis. It passes between the tunica arachnoidea 

 and pia mater, attached to the pia mater by cellular membrane. 

 It sends off a small process in a lateral direction, to be attached 

 to the dura mater in the interstices between the places where 

 the fasciculi pass through the dura mater, and nearly in the 

 middle between the upper and lower fasciculi. 



The spinal marrow terminates in a point near the uppermost 

 lumbar vertebra. The ligamenta denticulata of the opposite 

 sides join together at this point, and form a small chord, which, 

 continuing downwards, is inserted into the os coccygis. 



These ligaments may support, and keep fixed, the medulla 

 and the nerves, as they originate from it. 



As the spinal marrow terminates at the upper lumbar verte- 

 bra the lumbar and sacral nerves go off above: they pass 

 down like a bunch of straight twigs, and are called Cauda 

 Equina, from a fancied resemblance to the tail of a horse. 

 The sheath, formed by the dura mater for the spinal marrow, 

 continues of its original size, and encloses them in one cavity. 



The posterior and anterior fasciculi pass out separately from 

 the dura mater ; after they are out, the posterior fasciculus 

 forms a ganglion ; from which one nerve passes that joins the 

 anterior fasciculus, and thus forms the spinal nerves. 



When the nerves go off, either from the spinal canal, or the 

 cavity of the cranium, the external lamen of the dura mater 

 where they pass out, attaches itself to the bone or the peri- 

 osteum ; while an internal lamen, together with the pia mater, 

 and, perhaps, the tunica arachnoidea, is continued with the 

 nerve. 



