318 ^Journal of Comparative Neurology and Psychology. 



relatively very feebly developed. From the sixth lobe massive 

 tracts run caudad in the spinal cord, which is much larger than 

 usual among teleosts, though the remaining nerves are not greatly 

 enlarged. This enlargement is seen in the dorsal, dorso-lateral 

 and ventro-lateral tracts, including the funiculi proprii, but does 

 not involve the ventral funiculi. This would imply that reflex 

 movements of the trunk musculature habitually follow tactile 

 stimulation of the free pectoral fin rays, an inference which is sub- 

 stantiated by observations made on the living fish. But as we 

 pass toward the head from the first accessory lobe, there is evident 

 very little modification of the central nervous system due to the 

 enlargements of the spinal cord. These facts show that the 

 reflexes connected with the free pectoral fin rays are of the sim- 

 plest type, not involving extensively the higher cranial centers. 



The relations described in the preceding paragraph seem to be 

 merely a special case under the general rule formulated by Sher- 

 rington ('06), where he says (p. 58), "Broadly speaking, the 

 degree of reflex spinal intimacy between afferent and efferent spinal 

 roots varies directly as their segmental proximity. * * * 

 The spread of short spinal reflexes in many instances seems to be 

 rather easier tailward than headward. * * * Taken generally 

 for each afferent root there exists in immediate proximity to 

 its own place of entrance in the cord [e. g., in its own segment) a 

 reflex motor path of as low a threshold and of as high potency as 

 any open to it anywhere." It is possible, too, that if an analogous 

 relation holds in the spinal cords of higher vertebrates, it may 

 have some bearing on the further fact brought out by Sherring- 

 ton (p. 241), that "spinal shock appears to take effect in the 

 aboral direction only." 



Associated with the first and second accessory lobes are the 

 large somatic commissural nucleus and commissura infima. A 

 short distance headward from this lobe there is a very highly 

 developed median funicular nucleus, the lateral nucleus not being 

 differentiated. This nucleus sends massive medullated tracts 

 into the commissura infima. 



The secondary connections of these extensive somatic sensory 

 centers at the lower end of the oblongata are mainly with the adja- 

 cent formatio reticularis, ventral cornua and dorso-lateral fas- 

 ciculus. No unusually large numbers of long tracts descend in 

 the ventral funiculi or ascend in the crossed fasciculus lateralis 



