THE WHITE MATTEE OF THE SPINAL MEDULLA. 



531 



Posterior- 

 median septum 



Gray commis- 

 sure 



Anterior median 

 fissure 



Posterior-lateral furrow 



Posterior column of 

 gray matter 



Retro-postero- 

 lateral group 

 of cells 



institute the white rami communicantes. ' They represent the splanchnic efferent 

 ibres of the medulla spinalis. 



Nucleus Dorsalis (O.T. Clarke's Column). This occupies the posterior column 

 ')f gray matter and is the niost conspicuous of all the cell-groups in the medulla. 

 :!t does not, however, extend along the whole length of the medulla; indeed it is 

 ilmost entirely confined to the " dorsal " region, which is the reason for the 

 tesignation "nucleus dorsalis." (When, in the recent revision of nomenclature, 

 he term " thoracic " was substituted for " dorsal " the revisers omitted to change 

 ':he name of this structure to " thoracic "). Above, it begins opposite the seventh or 

 'eighth cervical nerve, whilst below, it may be traced to the level of the second 

 .umbar nerve, where it disappears. In transverse section of the medulla it presents 

 in oval outline, and is seen in the median part of the cervix of the posterior column 

 pf gray matter, immediately behind the gray commissure (Fig. 469, p. 530). On 

 the lateral side it is circumscribed by numerous curved fibres from the entering 

 posterior nerve-root, and in the lower thoracic region of the spinal medulla 

 ^opposite the eleventh and 

 twelfth thoracic nerves) 

 it becomes so marked that 

 it forms a bulging on the 

 median aspect of the pos- 

 terior gray column. 



The cells of the nucleus 

 dorsalis are large, and pos- 

 sess several dendritic pro- 

 cesses. The axons enter 

 the lateral funiculus of 

 white matter and there 

 form a strand of fibres, 

 which will be described 

 later under -the name 

 of the fasciculus spino- 

 cerebellaris (wrongly called 

 " cerebellospinalis " in the 

 B.N.A.). 



Nerve -fibres in the 

 Gray Matter of the 

 Medulla Spinalis. 

 Nerve-fibres of both the 

 medullated and the non- FIG. 

 medullated variety per- 

 vade every part of the 

 gray matter. They are of three kinds, viz., (1) collaterals, (2) terminations of nerve- 

 fibres, (3) axons given off by the cells. Many of the nerve-fibres which compose 

 the funiculi of the medulla give off numerous fine collateral branches, which pass 

 into the gray matter from all sides and finally end in relation with the nerve- 

 cells. The majority of the nerve-fibres themselves, which thus give off collaterals, 

 finally enter the gray matter, and end similarly. The axons of the majority of 

 the cells leave the gray matter and emerge either for the purpose of entering a 

 peripheral nerve or for the purpose of entering a strand of fibres in the white 

 matter of the spinal medulla. 



The nerve-fibres thus derived are interwoven together in the gray matter in a 

 dense inextricable interlacement. 



Postero-lateral group 

 of cells 



Central group of cells Antero-lateral group of cells 



471. SECTION THROUGH THE FIRST SACRAL SEGMENT OF THE 

 SPINAL MEDULLA TO SHOW THE GROUPING OF THE MOTOR NERVE- 

 CELLS. (To a large extent founded on Plates in Dr. Bruce's Atlas. ) 



COMPONENT PARTS OF THE WHITE MATTER OF THE SPINAL MEDULLA. 



The white matter of the spinal medulla is composed of medullated nerve-fibres, 

 embedded in neuroglia. The fibres, for the most part, pursue a longitudinal course ; 

 and, from the deep surface of the pia mater which surrounds the medulla, fibrous 

 septa or partitions are carried in along vertical planes between the fibres so as 



