796 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



size in proportion to the number of nerves entering into it ; and that> 

 therefore, the spinal cord should be largest in the cervical portion and 

 gradually taper down to a point in the lumbar region, as if each spinal 

 nerve were a direct loss to the fibres of the spinal cord. Such is not, 

 however, the fact. 



Sections of the spinal cord taken at different parts of its length 

 indicate that the gray matter of the cord increases with the amount of 

 nerve-fibre passing into each part of the cord, and that, therefore, the 

 largest amounts of gray matter are found in the lumbar and cervical 

 regions at the points of origin of the nerves for the lower and upper 

 extremities ; while, if the proportionate area of the lateral columns is com- 

 pared, it will be found that there is a steady increase in the sectional area 

 of this portion of the cord from the lumbar to the cervical region. This 

 fact would indicate that the latter regions are the main paths of con- 

 duction between the brain and the periphery. The proportion between 



FIG. 337. DIAGRAM OF THE ABSOLUTE AND RELATIVE EXTENT OF THE 

 GRAY MATTER AND OF THE WHITE COLUMNS, IN SUCCESSIVE SEC- 

 TIONAL, AREAS, AS WELL AS THE SECTIONAL AREAS OF THE NERVE- 

 ROOTS. (Landois. ) 

 N B, nerve-roots; A C, L C, P C, anterior, lateral, and posterior columns; Gr, gray matter. 



different parts of the spinal cord in the different regions and the different 

 areas of the spinal nerves are indicated in the diagram (Fig. 337). 



In addition to the anatomical division, already alluded to, into 

 anterior, lateral, and posterior columns, the white fibres of the spinal 

 cord have been divided into several secondary columns, according to 

 their functions. In addition to the experimental method, to be alluded 

 to directly, this grouping of the longitudinal fibres of the spinal cord 

 into different systems has been reached through facts acquired through 

 the study of the degeneration of certain parts after specific injury and 

 through the developmental history of the cord in the embryo. Thus, 

 injury of certain parts of the brain is followed by a secondary descending 

 degeneration of certain nerve-fibres (Tiirck) ; section of the cord causes 

 ascending degeneration of certain fibres (Schieferdecker) ; and Flechsig 

 showed that the fibres of the brain and cord in the embryo became 



