50 THE BRAIN OF THE TIGER SALAMANDER 



of efferent discharge from the dorsal thalamus go backward to the 

 peduncle and tegmentum by both crossed and uncrossed tracts (figs. 

 15, 18, 21, 23). The peduncular connection puts all the primary sys- 

 tems of total-pattern type under some measure of thalamic control. 

 The connections with the dorsal and isthmic tegmentum probably 

 co-operate in the patterning of local reflexes, particularly supplying 

 the visual component of the feeding reactions. 



0. PEDUNCLE 



The "peduncle" described here is not the equivalent of the human 

 cerebral peduncle (p. 21). The intimate relations of this field with 

 the overlying tecto-thalamic field have been commented upon in the 

 preceding paragraphs. This ventral field is a well-defined column of 

 cells, differentiated at the anterior end of the basal plate of the 

 embryonic neural tube. It is the head of the primary motor column 

 (of Coghill), which in all vertebrates, from early embryonic stages to 

 the adult, contains the nucleus of the oculomotor nerve and a much 

 larger mass of nervous tissue, which activates the primitive mass 

 movements of locomotion. It maintains cerebral control of the lower 

 bulbo-spinal segments of the latter systems, and some other motor 

 functions also are represented here. Into it fibers converge from all 

 other parts of the cerebrum (figs. 12, 14, 15, 17, 18, 20-24), and from 

 it efferent fibers go out in four groups: (1) Ventromedial tracts go 

 to the medulla oblongata and spinal cord. The longest of these fibers 

 are in the f. longitudinalis medialis (fig. 6). (2) The oculomotor nerve 

 supplies intrinsic and extrinsic muscles of the eyeball (figs. 22, 24). 

 Associated with these peripheral fibers are central connections with 

 the nuclei of the IV and VI nerves, so arranged as to execute conju- 

 gate movements of the eyes. The details of the apparatus employed 

 are unknown. (3) Visceral sensory and gustatory fibers enter the 

 peduncle (fig. 8), and with these are related efferent fibers to the hy- 

 pothalamus and to lower levels of the motor zone, The pathways 

 taken by the latter in the amphibian brain have not been clarified. 

 (4) From both ventral thalamus and peduncle, fibers diverge to 

 various surrounding parts, notably to the hypothalamus and isthmic 

 tegmentum. These probably provide for co-ordination of various 

 local reflex activities with the basic peduncular functions. 



At the ventrolateral border of the peduncle there is an area of 

 superficial neuropil, which is the terminus of the basal optic tract, 

 large secondary and tertiary visceral-gustatory tracts, some fibers of 

 the f. retroflexus, and fibers from several other sources (figs. 22, 23, 



