JOHN J. MASON. 



IV. ALLIGATOR MISSISSIPIENSIS. 



Spinal cord, cervical enlargement 



lumbar 

 Centre of motor cord of the trigeminus 

 " motor portion of the vagus 

 oculomotorius 

 Large cells of the raphe 

 Nuclei of eminentia acoustica 

 Sensitive cells of the vagus 

 Large cells of the cerebellum 

 Cerebrum and corpus striatum . 

 Optic tubercles 



6.5 X7-5 

 6-5 X 7-5 



6. X 7. 

 5-5x6. 

 5. x5. 



7. x8. 



3-5x4-5 

 3-5 X4.5 

 3-5 X4-5 

 3-5 X 4-5 

 2-5 X3- 



V. HELODERMA SUSPECTUM. 



With the exception of the caudal region of the spinal cord, 

 where much the same scarcity and successive reduction of size of 

 the nuclei exist as in the turtle, the diameters hold the same rela- 

 tion to each other as noted in the alligator. This remark also 

 applies to the nuclei of Scincus Erythrocephalus. 



VI. — ■ Em.rTIIROCEriIALU&. 



The nerve cell nuclei of small specimens are notably smaller 

 than the corresponding nuclei of larger specimens of the same 

 order. This rule only applies to orders, for some of the nuclei of 

 Rana Pipiens, from the spinal cord, measure as much as those of 

 the 24-pound turtle. The nuclei of the small lizards are, as a 

 whole, proportionally larger than those of heloderma or the alligator. 



The proposed law, formulated in my last paper, may now 

 read as follows : 



The nuclei of the so-called motor cells of the central nervous 

 system have, in the same individual, average diameters, zvhich 

 are proportional to the poiver developed in the related mus- 

 cles. 



The writer, in conclusion, while admitting the incom- 

 pleteness of his work, must at least claim to have demon- 

 strated the fact that a hitherto unobserved relation exists 

 between the size of a motor nucleus and that of its periph- 

 eral organ, the muscle. 



