522 



THE NEEVOUS SYSTEM. 



CVi 



Posterior median 

 septum 



Cervical swelling 



Sulcus inter- 



medius posterior 



Posterior lateral 

 sulcus 



-THVn 



medulla are made, it is seen to be a bilateral structure which is partially subdivided 

 into a right and a left half by a median cleft (fissura 

 mediana anterior) in front and a septum (septum medianum 

 posterius) behind. The anterior median fissure penetrates 

 only for a distance corresponding to somewhat less than 

 a third of the antero-posterior diameter of the spinal 

 medulla. The pia mater dips down into it and forms a 

 fold or reduplication within it. The posterior median 

 septum in the cervical and thoracic regions penetrates into 

 the spinal medulla until it reaches a point somewhat 

 beyond its centre. It is extremely narrow, and consists oi 

 ependymal and neuroglial elements, and is intimately con- 

 nected with the adjacent sides of the two halves of the 

 spinal medulla, between which it intervenes. The pia 

 mater, which invests the surface of the spinal medulla 

 passes continuously over the posterior median septum 

 and sends no prolongation of any kind into it. In the 

 lumbar region of the spinal medulla the septum becomes 

 shallower, whilst the anterior median fissure deepens, and 

 ultimately in the inferior part of the spinal medulla the 

 fissure and septum present a very nearly equal depth. 



The two halves of the spinal medulla may show 

 trifling differences in the arrangement of the parts which 

 compose them ; but to all intents and purposes they are 

 symmetrical. They are joined together by a more or less 

 broad band or commissure, which intervenes between the 

 median fissure and the septum. 



An inspection of the surface of each half of the spinal 

 medulla brings into view a longitudinal groove or furrow 

 at some little distance from the posterior median septum 

 which extends along the whole length of the spinal medulla 

 Along the bottom of this groove the fila of the posterioi 

 nerve-roots enter the spinal medulla in accurate linea; 

 order. It is called the sulcus lateralis posterior. Therr 

 is no corresponding furrow on the anterior part of eacl 

 half of the spinal medulla in connexion with the emergcnc 

 of the fila of the anterior nerve-roots. These fila emerg 

 irregularly over a broad strip of the surface of the spina 

 medulla, which corresponds in its width to the thicknes 

 of the subjacent anterior surface of the anterior column c 

 gray matter. 



The sulcus lateralis posterior subdivides each half ( 

 the spinal medulla into a small funiculus posterior and 

 much larger antero-lateral funiculus, and it is customai 

 to map the latter arbitrarily off into a funiculus lateral 

 and a funiculus anterior by a line corresponding to tl 

 emergence of the most lateral of the fila or fascicles of tl 

 anterior nerve-roots. 



In the cervical region a distinct longitudinal grocr 

 may be observed on the surface of the posterior funicuh 

 It is placed rather nearer to the posterior median septu 

 than to the posterior lateral sulcus, and as it is trac 

 down into the thoracic region it gradually becomes i 

 distinct and finally disappears. This is called the sulc 

 mtermedius posterior, and it marks on the surface t 

 position of a septum of pia mater which dips into t ! 



spinal medulla and subdivides the posterior funiculus into a lateral part, term 



the fasciculus cuneatus (O.T. column of Burdach), and a medial portion, which recer ' 



the name of the fasciculus gracilis (O.T. column of Goll). 



Lumbar swelling- 



-THVx 



-THVxu 



LVn 



FIG. 465. DIAGRAM OF THE 

 SPINAL MBDULLA AS SEEN 

 FROM BEHIND. 



CVi shows the level of the 1st 

 cervical vertebra ; CVv of the 

 5th cervical vertebra ; THVn 

 of the 2nd thoracic vertebra ; 

 THVx of the 10th thoracic 

 vertebra ; THVxn of the 12th 

 thoracic vertebra ; LVn of the 

 2nd lumbar vertebra. 



