42 THE BRAIN OF THE TIGER SALAMANDER 



of local reflexes of the limbs and the integration of these reflexes with 

 one another and with the action of the trunk musculature, as in 

 ordinary locomotion. 



"l. THE BULBO-SPINAL JUNCTION 



The sector of the bulbo-spinal junction includes the upper seg- 

 ments of the spinal cord and the lower part of the medulla oblongata. 

 It is the first center of correlation to become functional in embryonic 

 development (Coghill, '14, Paper I). Its dorsal part around the 

 calamus scriptorius receives fibers from the entire sensory zone of the 

 bulb and cord, so that this gray of the funicular and commissural 

 nuclei is a general clearing-house for all exteroceptive, propriocep- 

 tive, and visceral functions of the body except vision and olfaction. 

 Here these functions are integrated in the interest of control of pos- 

 ture, locomotion, visceral activity, and other basic components of 

 mass-movement type. Some of these connections are shown diagram- 

 matically in figures 3, 7, 8, 87; for details and discussion see chapter 

 ix and a recent paper ('446). 



Efferent fibers from the dorsal nuclei are directed spinalward and 

 forward. Most of the latter connect with motor nuclei of the medulla 

 oblongata; some go farther forward to the cerebellum, tectum, and 

 thalamus; and there is a strong, ascending visceral-gustatory tract 

 to the isthmus and peduncle. The motor zone of this sector is occu- 

 pied chiefly by fibers of passage. The moderately developed gray sub- 

 stance includes motor neurons for muscles of the neck region, for the 

 tongue muscles, and for special visceral motor elements of the ac- 

 cessorius component of the vagus. 



3. MEDULLA OBLONGATA 



The medulla oblongata, or bulb, includes all the stem between the 

 isthmus and the calamus scriptorius except the cerebellum, there 

 being no pons. Its dorsal field receives all sensory fibers from the 

 head except the optic and olfactory, fibers from lateral-line organs 

 widely distributed over the body, and general visceral sensory fibers 

 chiefly by way of the vagus. The general visceral sensory and gusta- 

 tory root fibers are segregated from the others in the fasciculus 

 solitarius; and this group has its own system of secondary fibers, 

 which converge into the visceral motor nuclei of the medulla ob- 

 longata and spinal cord. There is also a strong ascending secondary 

 visceral tract {tr.v.a.) to the isthmus, peduncle, and hypothalamus, 

 through which all cerebral activities may be influenced by visceral 

 and gustatory functions (fig, 8 and chaps, x, xi). 



