II CENTRAL NERVOUS SYSTEM. 



and nucleoli are plainly visible, may be taken as a type of what is al- 

 ways found in the enlargements of the spinal cord of reptiles and ba- 

 trachians. 



It is uncertain whether the striation of the cell-body, Plate CIX., 

 denotes true fibrillar structure, or is due to the action of reagents. 



Besides the group of large cells, there are many small ones scattered 

 through the gray substance. These are more abundant in batrachians 

 than in reptiles proper, and their nuclei are often difficult to distinguish 

 from those of the connective tissue. The latter are verj' prominent ob- 

 jects in sections from tailed batrachians, appearing conspicuously in both 

 the white and gray substances. 



In Plate V. i-iii — alligator 3 mos. old — these nuclei are shown as 

 small, dark objects especially abundant in the white substance. See al- 

 so Plate XCIX. in which the difference between the small ner\-e cells 

 and the elements of connective tissue is quite apparent. 



Ner\-e cells of middle size, with nuclei of corresponding dimensions, 

 are also found in various parts of the gray substance, but never as a dis- 

 tinctly limited group, with the exception of the dorsal region of the frog, 

 where thej- appear as represented in Plates XXIX. & XXX. just above 

 the level of the central canal, one group on each side of the substantia 

 reticularis. These cells were described by me in the New York Medi- 

 cal Journal for December, 1879, with a hint as to their possible homol- 

 ogy to the columns of Clarke. 



The fibres in the gray substance, exclusive of those which belong 

 to the connective tissue, are very abundant, and especially so in the al- 

 ligator and turtle. Plates I. & II. from chromic acid preparations give 

 an idea of the structure, in this respect, of the inferior horns ; the bun- 

 dles running in many directions, and being as large as the fibres of the 

 inferior roots. Plates XVI. & XVIII. from preparations hardened in 



-A- 



