182 WILLIAM F. ALLEN 



tissue capsule. In the middle spindle which happens to be cut 

 longitudinally, three muscle fibers and a portion of the spiral or 

 annular placque (PL) are represented in figure 14 as they appeared 

 in the section, while the connective tissue capsule (Cap.) is 

 seen to be poorly developed. The lowermost spindle is cut 

 transversely through its distal end. Its tendinous bundle 

 (Ten.) took the haematoxylin stain strongly and is enveloped 

 in a conspicuous lamellated connective tissue sheath. 



REMARKABLE SIZE OF CERTAIN MOTOR FIBERS IN THE SPINAL 



NERVES 



Certain structures, which were at first taken to be peripheral 

 ganglion cells, appeared in transverse section of the rami ven- 

 trales of the Polistotrema from which figure 5 was reconstructed. 

 Upon closer examination no nuclei were found in these struc- 

 tures, and they are evidently the axones of certain large motor 

 cells in the spmal cord. In order that a direct comparison of 

 the size of these fibers might be made mth the largest fibers of 

 other nerves, figure 18 was constructed, using a magnification 

 of 100 diameters in each case. The above mentioned colossal 

 fibers appear in transverse (fig. 18, B.) , from which it will be seen 

 that these fibers are enormous when compared to the largest fibers 

 of the vagus and glossopharnygeal nerves (fig. 18, A. and C). 

 In figure 18 a direct comparison can also be made of the size of 

 the largest fibers (D.) from the ramus ventralis of the spinal 

 nerve reconstructed in figure 4 with the much smaller sensory 

 fibers {E.) from the sensory ramus dorsalis of the same nerve 



In turning to the literature on this subject it was of especial 

 interest to find that Johnston ('08) had called attention to the 

 large size of the few fibers found in the ventral motor rami of 

 the spijial nerves of Petromyzon The enormous caliber of 

 these nerve fibers is attributed by Johnston to the fact that, 

 since there are relatively very few fibers in a ventral motor 

 ramus, each fiber must necessarily supply a great number of 

 muscle fibers. 



What significance then can be attached to the enormous 

 caliber of the motor spinal nerve fibers in Polistotrema? Appar- 



