10 , THE SPINAL COED. 



The lateral symmetry of the spinal cord is not always perfect. The white columns 

 especially are found slightly to vary, the variation being generally caused by the 

 fact that the amount of the pyramidal tracts of white matter differs somewhat on 

 the two sides of the cord (see p. 24). More rarely considerable malformations 

 have been found to occur. 



The white matter of the cord, especially that of the lateral and posterior columns, 

 increases gradually in amount from below upwards, receiving a considerable accession 

 opposite the roots of the larger nerves which supply the limbs. These relations are 

 strikingly shown in the appended curves (fig. 10) which have been constructed by 

 Ludwig and "Woroschiloff from measurements by Stilling. The amount of the grey 

 matter in the different regions is also given, as well as the sectional areas of the 

 roots of the spinal nerves. It is seen that opposite to the origins of the large nerves 

 there is a marked increase in the amount of grey matter. 



The anterior or white commissure is likewise proportional in size to the entering 

 nerve-roots. 



Characteristic features of the different regions of the cord. In the 

 sacro-coccygeal region the bulk of the spinal cord is formed of grey matter which 

 has a comparatively thin mantle of white substance surrounding it. The posterior 

 cornua are nearly as thick as the anterior, and the isthmus of grey matter is relatively 

 thick. The lateral cornu (in the sacral region) is well marked. Both here and in 

 the lumbar region the number of nerve-cells imbedded in the grey matter is rela- 

 tively very large, a fact which is probably connected with the circumstance that 

 these regions are concerned with numerous and important reflex acts. 



In the lumbar region the white matter begins to predominate, owning chiefly to 

 the accession of the large nerve-roots of the sacral and lumbar plexus, many of the 

 fibres to and from which are now running down and up the white columns of the 

 cord. The posterior horn and the grey matter in general is still thick, although in 

 the upper part of the lumbar region it has become thin and has more of the 

 character which is met with in the thoracic region. The lateral horn is not distinct. 

 The outline of the cord is beginning to be more circular, a shape which is maintained 

 as far as the second thoracic segment. 



In the dorsal or thoracic region the chief characteristic is the relatively small 

 amount of grey matter, which forms two long slender crescents united by a narrow 

 isthmus, which both here and in the cervical region is placed nearer the ventral than 

 the dorsal aspect of the cord, whereas in the lumbar and sacral regions it lies near 

 the middle of the dorso-ventral axis. The white matter is absolutely as well as 

 relatively greater in amount than in the lumbar region. The lateral horn forms a 

 distinct acute prominence throughout the whole of the thoracic region, but is most 

 marked in the upper part. Clarke's column (see p. 10) is also to be seen near the 

 base of the posterior horn : it is most prominent at the lower part of the thoracic 

 region. In the upper part the postero-mesial column begins to be marked off from 

 the postero-lateral. 



The cervical region is characterized by the fact that the cord, except at the upper- 

 most part, is of large size and tends to be somewhat flattened dorso-ventrally. The 

 increase in size affects both grey and white matter. The postero-mesial column is 

 now sharply marked off from the postero-lateral. Fibres of the spinal accessory 

 roots may be seen passing out from the lateral cornu. A reticular formation is seen 

 at the outer edge of the grey matter. Both the lateral and anterior cornua are large 

 and are fused together to form a mass of grey matter, triangular in section, and 

 tapering off dorsally into the base of the posterior horn. This horn and the substance 

 of Rolando are but slenderly developed, contrasting with the large development of 

 the same parts in the lumbar enlargement. The isthmus is thin, and the central 

 canal flattened dorso-ventrally. 



