4 NERVOUS SYSTEM OF REPTILES AND BATRACHIANS. 



must have great weight against the conclusion that only 

 the large nerve cells are connected with motor fibres." 

 Accepting the passage as it stands I agree with him, but he 

 has not fairly stated the ordinary view. It does not seem 

 to me that " only the large nerve cells are connected with 

 motor fibres," represents fairly the prevailing belief of 

 anatomists and physiologists. That all the large nerve 

 cells are thus connected is more accurately what is thought 

 to be the fact. Of course, no one has ever claimed that 

 the cells of origin of the oculomotorius, for example, 

 were large cells or doubted that they were in connection 

 with the fibres of the third pair of cranial nerves. Nerve 

 cells, therefore, may be small and still be connected with 

 motor nerve filaments. In the dorsal and caudal regions of 

 the spinal cord of turtles the motor cells are small, because 

 the muscles which they innervate are small. At the same 

 time, it may be true that all large cells connect with motor 

 filaments. To me, this is all in favor of ascribing difference 

 in energy to different-sized cells or rather nuclei. The 

 nucleus can be accurately measured, while the body of the 

 cell can not be, and as the former probably constitutes the 

 true cell, it has been preferred as an object of study in 

 my researches. 



MEASUREMENTS OF THE DIAMETERS OF THE NUCLEI OF NERVE 

 CELLS WHICH ARE RELATED TO THE MOTOR FIBRES OF THE CRA- 

 NIAL NERVES. 



I. In four species of turtle, viz.: (i) Emys Floridana, 

 (2) Emys Terrapin, (3) Testudo Polyphemus, and (4) Chely- 

 dra Serpentina, the following have been found to be the 

 comparative dimensions of these nuclei : 



The largest nuclei are found in the cells of the spinal 

 cord and those of the nucleus basilaris of Stieda. Next to 

 these in size are those of the centre for the motor root of 

 the trigeminus, supplying with its fibres the elevator mus- 



