HISTOLOGICAL STRUCTURE 3r> 



acquired patterns of behavior (Economo, '26, '29). No mathematical 

 precision should be claimed for these laws, but they do express the 

 general trend of our experience. For additional data and critical 

 comment see von Bonin on page 64 of the monograph by Bucy and 

 others ('44). 



The properties of amphibian neuropil have been discussed in sev- 

 eral places, in addition to the summary already cited ('42, p. 199). 

 In one of these papers ('33c?) the geniculate neuropil of Necturus was 

 described, and later ('42, p. 280) the quite different arrangement of 

 Anibly stoma (compare the corresponding structure of the frog, '25), 

 together with a full account of the neuropil of the optic tectum and 

 its connections (here, again, comparison with the more differentiated 

 structure of the frog is instructive). In connection with a general 

 survey of the neuropil of Necturus, its peculiar relations in the pallial 

 part of the hemisphere were discussed in four papers ('336, p. 176; 

 '336?, '34, '34a). Amblystoma is similar ('27), though the details have 

 not been fully explored. In the pallial field the four layers of neuropil 

 tend to merge into a single apparatus of association. This is cortico- 

 genetic tissue within which the earliest phases of incipient differentia- 

 tion of laminated cortex can be recognized in the hippocampal area, 

 as described in chapter vii. 



Some samples of the appearance of elective Golgi impregnations of 

 amphibian neuropil are shown in the accompanying illustrations, and 

 many others are in the literature. The related morphological and 

 physiological problems can best be presented in the form of illustra- 

 tive examples, one of which is the striatal neuropil (chap, vii), an- 

 other the interpeduncular neuropil described in chapter xiv, and still 

 another in the superficial ventrolateral neuropil of the peduncle, 

 the area ventrolateralis pedunculi, which will next be described. 



THE VENTROLATERAL PEDUNCULAR NEUROPIL 



The "peduncle" in the restricted sense as here defined, together with the adjoining 

 tegmentum, is the chief central motor pool of the skeletal muscles. Efferent fibers 

 from it are among the first to appear in the upper brain stem in embryogenesis, 

 descending in the primary motor path, which is the precursor of the fasciculus 

 longitudinalis medialis, and activating the musculature of the trunk. A second 

 efferent path, which appears very early, goes out directly to the periphery through 

 the oculomotor nerve. The first sensory influence to act upon this pool comes from 

 the optic tectum through the posterior commissure in the S-reaction stage. In sub- 

 sequent stages it is entered by fibers from many other sources, including the basal 

 optic tract (fig. 14) and the olfacto-peduncular and strio-peduncular tracts (fig. 6). 

 In the adult animal, motor impulses issuing from this pool are probably concerned 



