THE SPINAL MEDULLA. 



523 



Fasciculus gracilis 

 Posterior funiculus ^=-^^ Fasciculus cuneatus 



Anterior 

 nerve-root 



INTERNAL STRUCTURE OF THE SPINAL MEDULLA. 



The spinal medulla is composed of a central core of gray matter thickly coated 

 m the outside by white matter. At only one spot does the gray matter come close 

 ;o the surface, viz., at the bottom of the sulcus lateralis posterior. 



Gray Matter of the Spinal Medulla. The gray matter in the interior of the 



spinal medulla has the form of a fluted column, but it is customary to describe it 



is it appears in transverse sections. It then presents the appearance of the 



'iapital letter H. In each half of the spinal medulla there is a semilunar or 



.irescen-tic mass, shaped somewhat like a comma, the concavity of which is directed 



laterally and the convexity medially. The two crescents of opposite sides are con- 



lected across the median plane by a transverse band, which receives the name of 



;he commissura grisea (gray commissure). The posterior median septum extends 



brwards in the spinal medulla until it reaches the gray commissure. The bottom 



>f the anterior median fissure, however, is separated from it by an intervening 



.trip of -tthite matter, which is termed the commissura anterior alba, or anterior 



vhite commissure. In the gray commissure may be seen the central canal of 



he spinal medulla (canalis centralis), which tunnels the entire length of the 



.pinal medulla and is just 



dsible to the naked eye as 



, minute speck. The por- 



ion of the gray commis- 



ure which lies behind the 



entral canal is called Formatio reticularis 



.he commissura posterior; Lateral funicu i us 



Whilst the portion in front Central canal 



eceives the name of the Accessory root 



ommissura anterior grisea. Origin of accessory 



Each crescentic mass of 

 (ray matter presents cer- 

 i ain well - defined parts. 



^he projecting portions Anterior funiculus 



rilich extend behind and FIG. 466. TRANSVERSE SECTION THROUGH THE SUPERIOR PART OF THE 



1 front of the connecting CERVICAL REGION OF THE SPINAL MEDULLA OF AN ORANG. 



VPTXP o-rnvrnm -nrp (From a s P ecimeu prepared by the Weigert-Pal method, by which 



gray C < the white matter . g rendered dark whilst the ^^ matter is bleached. ) 



re termed respectively the 



osterior and the anterior columns of gray matter (columnae grisese). These stand 

 ut in marked contrast to each other. In section the columna anterior is short, 

 hick, and very blunt at its extremity. Further, its extremity falls considerably 

 hort of the surface of the spinal medulla and is separated from it by a moderately 

 hick coating of white matter. Through this the fila of the anterior nerve-roots, 

 s they emerge from the gray matter of the anterior column, pass on their way to 

 he surface. Throughout the greater part of the spinal medulla the columna posterior 

 3.T. posterior cornu) is elongated and narrow, and is drawn out to a fine point, which 

 ilmost reaches the bottom of the posterior lateral sulcus. This pointed extremity 

 iceives the name of the apex columnse posterioris ; the slightly swollen part which 

 icceeds it is the caput columnse; whilst the slightly constricted part adjoining 

 ie gray commissure goes under the name of the cervix columnae posterioris. 



The apex or tip of the posterior column differs considerably in appearance from 



ie general mass of the gray matter. It is composed of a material which presents 



lighter hue and has a somewhat translucent look. It is called the substantia 



,3latinosa [Rolandi], and, when seen in transverse section, it exhibits a V-shaped 



itline and fits on the posterior column like a cap. 



A pointed and prominent triangular projection juts out from the lateral 

 5pect of the gray matter nearly opposite the gray commissure. This is the columna 

 .teralis (O.T. lateral cornu), and it is best marked in the upper thoracic region 

 ?ig. 467, B). Traced upwards it becomes absorbed in the greatly expanded anterior 

 )lumn of the cervical swelling, but it reappears again in the upper part of the 

 )inal medulla, and is particularly noticeable in the second and third cervical 



