THE GKAY MATTEE OF THE SPINAL MEDULLA. 



529 



he arrangement of the axons of the great majority of the motor cells, it should be 

 oted that a few cross the median plane in the anterior white commissure and 

 merge in the fila of origin of the opposite anterior nerve-root. 



The ventral cells are not scattered uniformly throughout the anterior column of gray 

 latter. They are aggregated more closely together in certain parts of the anterior column, 

 , nd thus form sub-groups or columns more or less perfectly marked off from each other. 



Thus, one sub-group or column of ventral cells occupies the medial part of the anterior 

 olutnn of gray matter throughout almost its whole length. In only two segments of the 

 aedulla is it absent, viz., the fifth lumbar and the first sacral ; at this level in the spinal 

 aedulla alone is its continuity broken (Bruce). It is termed the antero-median column or 

 roup of ventral cells. Behind this cell-column there is another classed with it to which 

 'he name of postero-median column or group is given, but this column of cells is not con- 

 ! inuous throughout the entire length of the medulla. It is present in the thoracic region of 

 he spinal medulla, where the motor nuclei for the muscles of the limbs are absent; and 

 t is seen also in two or three of the segments of the cervical region and in the first 

 umbar segment (Bruce) ; elsewhere it is not represented. 



In the cervical and lumbar swellings of the medulla, where the marked lateral out- 



Posterior lateral furrow 



Posterior column of 

 gray matter 



Posterior median septum 



*ray commissure 



Postero-lateral 

 motor cells 



Anterior median 

 fissure 



Antero-median group 

 of motor cells 



Antero-lateral 

 group of motor cells 



FIG. 468.- 



-SECTION THROUGH THE FIFTH CERVICAL SEGMENT OF THE SPINAL MEDULLA. 

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



growth is added to the lateral side of the anterior column of gray matter, certain groups of 

 large multipolar cells are visible. These are the nuclei of origin of the motor-fibres which 

 supply the muscles of the limbs, and consequently they are riot represented in the upper 

 three cervical segments of the spinal medulla ; nor in any of the thoracic segments, with 

 the exception of the first thoracic segment ; nor in the lowest two sacral segments. 



These lateral cells are arranged in several columns, which extend for varying distances 



in the superadded lateral parts of the anterior column of gray matter. The two main 



Columns are an antero-lateral and a postero-lateral column; in certain segments there is 



likewise a retro-postero-lateral column, and in a number of segments in the lumbar and sacral 



: regions a central column of cells (Bruce). 



There cannot be a doubt that the grouping of the motor cells in the anterior column of 



?ay matter of the medulla stands in relation to the muscle groups to which their axis-cylinder 



Jsses are distributed ; but from what has been said it will be apparent that sharply 



efined cell -clusters associated with particular muscles do not exist. Still, much can be 



iarned regarding the localisation of the motor nuclei in the anterior column of gray 



;ter of the medulla from the study of the changes which occur in the cell-columns after 



;rophy of isolated muscles or groups of muscles, and after complete or partial amputa- 



is of limbs. It has been pointed out that the long muscles of the trunk (as, for 



example, the different parts of the sacro-spinalis muscle) receive nerve-fibres from all the 



35 



