4 Mason — Central Nervous System of Reptiles, etc. 



twentj-fonr sections, from the middle of tlie brachial enlaro;e- 

 ment of Rana halecina, I counted in both inferior horns 540 

 large and medinm-sizod nuclei, and in an unbroken series of 

 twenty-four sections from the middle of tlie crural enlarge- 

 ment I counted in both horns 390 nuclei. Heissner * esti- 

 mated the lengtli.of the brachial enlargement as standing to 

 that of the crural enlargement in the ratio of 6-10, and this 

 proportion is true of the American species, as would be sup- 

 posed. It seems fair to conclude therefore, that while the 

 crural enlargement in frogs has a smaller transverse diameter 

 than that of the bi-achial enlargement, still, by its greater 

 length it contains as many if not more ganglion cells than the 

 latter. It is then, perhaps, tlie lai-ger of the two swellings 

 and corresponds, as it ought, with the larger size of the poste- 

 rior extremities. 



The preponderance of the lumbar enlargement in birds, and 

 the equality of the two which I have observed in the alligatorf 

 and in several species of lizards can undoubtedly be explained, 

 by regarding the amount of grey matter, or possibly the num- 

 ber of nerve-cells, as the surer indication of importance of 

 function in diflferent regions of the cord. 



The large crural nerve cells, as well as their nuclei, are 

 larger than those of the hrachial region. 



This fact I have established l)y numerous measurements, 

 which may be condensed into the following average diameters 

 for Rana halecina: Brachial nuclei, long diameter, 7; crural 

 nuclei, long diameter, 8; bracliial nuclei, short diameter, 

 G.5 ; crural nuclei, short diameter, 7.5. The numbers denote 

 divisions of the micrometer eye-piece, each division with the 

 objective used representing .002 mm. 



After a thorough comparison of sections from the brachial 

 region of twenty large specimens of Rana pipiens, of which 

 seven were males, I have been unable to detect any difference 

 either in the arrangement, size or structure of the elements, 

 that could I'easonably be referred to as explaining the remark- 



* Loc. cit — Length of iutumesccnlia anterior, G mm.; that of intumcs- 

 centia posterior Id mm. 



f See " Transaclions of American Neurological Association," in preceding 

 number of the Jouknal. 



