458 



THE TISSUES. 



another portion of the motor fibres is continuous with the longi- 

 tudinal fibres of the same side, without any decussation. 



It should be added that though the motor fibres diminish in size 

 after entering the cord, till they enter the gray matter, where they 

 are about goW of an inch in diameter, they again enlarge as they 

 emerge from the latter, but never so as to attain their original dia- 

 meter. 



The sensitive roots also penetrate the white matter of the cord 

 to the posterior horns of the gray matter, and proceed, without 

 any direct connection with the nerve-cells, quite through the sub- 

 stantia gelatinosa into the sub- 

 stantia grisea. From this point 

 some of the fibres bend up- 

 wards nearly at a right angle, 

 and proceed to become longi- 

 tudinal fibres in the posterior 

 columns. Another portion of 

 them penetrates, in a fascicular 

 form, between the above-men- 

 tioned longitudinal bundles, fur- 

 ther forwards, losing themselves 

 in the posterior and the lateral 

 columns, and also extending 

 into the gray commissure pro- 

 bably on the opposite side. (Fig. 

 303.) 



The sensory fibres also de- 



column, with the sensitive roots (h), traversing it. Crease in size as they traverse 

 6. Substantia gelatinosa. c. Prolongations of the the cord tm th reach th 



nosterior roots, whifih band round in front, of tho <r 



gray commissures; being ygV^r 

 of an inch in the roots them- 

 selves, never more than 3 oV o of 

 an inch in the substantia gelati- 

 nosa, T2 J^ to 4^-0 of an inch 

 in the substantia grisea, and 

 only T 5 JOTT to T oio o f an inch 



in the gray commissure. They, however, also increase on leaving 

 the latter, to from T^J^ to g^ou f an inch, and afterwards become 

 longitudinal fibres. 



Besides the motor and sensory fibres, there are still others in the 



Vertical and antero-posterior section through the 

 cord, midway between the gray cornua and the point 

 of entrance of the roots of the nerves, a. Posterior 



posterior roots, which bend round in front of the 

 substantia gelatinosa, and run longitudinally in 

 order there to join more particularly the posterior 

 column, d. Basis of the posterior cornua, with the 

 ends of the horizontal portion of the sensitive roots 

 apparent (from their being cut across), e. Anterior 

 cornua, with the large nerve-cells (the spots), and 

 also the horizontal and divided continuations of the 

 motor roots. /. Anterior column traversed by the 

 motor roots (i) .Magnified 25 diameters. (Kulliker.) 



