INTERNAL STRUCTURE OF THE SPINAL CORD. 425 
of the cervical swelling, but it reappears again in the upper part of the cord about 
the level of the third cervical nerve; followed in a downward direction it blends 
with the anterior horn in the lumbar swelling and contributes to the thickening of 
that cornu. It is interesting to note that it again reappears in the sacral region. 
The gray matter is for the most part mapped off from the surrounding white matter 
with a considerable degree of sharpness; but in the cervical region, on the outer 
aspect of the crescentic mass and in the angle between the anterior and posterior 
horns, fine bands of gray matter penetrate the white matter, and, joining with each 
other, form a network the meshes of which enclose small islands of white matter. 
This constitutes what is called the formatio or processus reticularis. Although 
best marked in the cervical region, traces of the same reticular formation may be 
detected in the lower regions of the cord. 
Characters presented by the Gray Matter in Different Regions of the Cord. 
—The gray matter is not present in equal quantity nor does it exhibit the same form 
in all regions of the cord. Indeed, there is reason to believe that every cord segment 
presents its own special characters in both of these respects. It is not necessary, 
however, in the present instance to enter into this matter with any degree of 
minute detail. It will be sufficient if we point out the broad distinctions which 
are evident in the different regions. 
It may be regarded as a general law that, wherever there is an increase in the 
size of the nerves attached to a particular part of the cord, a corresponding 
increase in the amount of gray matter will be observed. It follows from this 
that the regions where the gray matter bulks most largely are the lumbar and 
the cervical swellings. The great nerve-roots which go to form the nerves of the 
large limb-plexuses enter and pass out from those portions of the cord. In the 
dorsal region there is a reduction in the quantity of gray matter in correspondence 
with the smaller size of the dorsal nerves. 
In the dorsal region (Fig. 320, B) both horns of gray matter are narrow, although 
the distinction between the anterior horn and the still more attenuated posterior 
horn is sufficiently manifest. In the cervical region (Fig. 320, A) the contrast between 
the cornua is most marked; the anterior horn is of great size and presents a very 
broad surface towards the anterior aspect of the cord, whilst the posterior horn 
remains narrow. In the lumbar region (Fig. 320, C), on the other hand, the 
difference in the breadth of the two gray horns is not so marked, owing to a 
broadening out of the posterior horn. The increase in the quantity of gray matter 
in the cervical swelling is chiefly confined to the anterior horns, whilst in the 
lumbar swelling it takes place in both horns. In the lower part of the conus 
medullaris the gray matter in each lateral half of the cord assumes the form of an 
oval mass joined to its fellow of the opposite side by a thick gray commissure. 
Here almost the entire bulk of the cord consists of gray matter, seeing that the 
white matter is reduced to such an extent that it forms only a thin coating on the 
outside. 
White Matter of the Spinal Cord—In transverse sections of the cord the 
three columns into which the white matter is subdivided become very apparent. 
The posterior column is wedge-shaped, and lies between the postero-median fissure 
and the posterior horn of gray matter. The lateral column occupies the concavity 
of the gray crescent. Behind, it is bounded by the posterior horn of gray matter 
and the postero-lateral sulcus, whilst in front it extends as far as the outermost 
fasciculi of the anterior nerve-roots as they pass out from the anterior gray horn. 
The anterior column includes the white matter between the antero-median fissure 
and the anterior horn of gray matter, and also the white matter which separates the 
broad extremity of the anterior gray cornu from the surface of the cord. This 
latter portion of the anterior column is traversed by the emerging fascicles of the 
anterior nerve-roots. 
In cross-sections of the cord the partition of pia mater, which dips in at the 
posterior paramedian groove and divides the posterior column into the column of 
Goll and the column of Burdach, is very strongly marked in the cervical region ; 
“but as it is traced downwards into the dorsal region it becomes shorter and fainter, 
and finally disappears altogether at the level of the eighth dorsal nerve. Below 
