190 THE BRAIN OF THE TIGER SALAMANDER 



acting through the ventral tegmental fascicles upon the lower bulbar 

 and spinal apparatus — and, since the isthmic tegmentum matures 

 later in development, with notable enlargement preceding meta- 

 morphosis, it seems safe to infer that the isthmic apparatus is the 

 chief regulator of the musculature concerned with feeding. The 

 courses of the efferent fibers from the isthmus support this supposi- 

 tion. In Ambly stoma the feeding activities are thoroughly integrated 

 movements, where posture of the body, conjugate movements of the 

 eyes, and action of jaws, pharynx, and esophagus are organized as a 

 "total pattern," as Coghill ('36) has demonstrated. For further con- 

 sideration of the olfactory and hypothalamic components of feeding 

 reactions see pages 210 and 252 and 19346, page 384. 



It is evident that control of feeding reactions is not the only function 

 of the isthmic sector. For instance, it has been shown by Aronson and 

 Noble ('45) that the removal of the entire brain of the male frog in 

 front of this region (including the tectum, cerebellum, and anterior 

 part of the tegmentum) did not interfere with spawning movements 

 but that "lesions in the tegmentum at the level of the motor nucleus 

 of the trochlear nerve markedly disturbed or completely abolished 

 these spawning responses." 



In addition to this apparatus of activation of behavior, there are in- 

 hibitory functions here also, implying a participation in motor con- 

 trol of wide import. The intricate connections of the isthmic teg- 

 mentum described in the next chapter are part of this inhibitory ap- 

 paratus. 



The unitary character of most of the activities of Amblystoma, 

 involving the synergic action of large masses of musculature in in- 

 variable orderly sequence, with relatively less capacity for the local 

 autonomous action of the individual members than in higher ani- 

 mals, explains the simplicity and relative homogeneity of the nerv- 

 ous apparatus involved — also why the isthmic tegmentum is so 

 large in Amblystoma. The integrated functional complexes which 

 here are controlled from this major pool are individually differenti- 

 ated in man, with corresponding specialization and segregation of 

 the apparatus of the several component parts; and, parallel with this 

 differentiation and increase of local autonomy, the central control 

 apparatus has been transferred from the stem to the cerebral cortex. 

 Accordingly, the isthmic tegmentum, which bulks so large in the 

 brain of Amblystoma (and in the early human embryo), is dismem- 

 bered in the adult man, and its parts are submerged within surround- 

 ing, structures. 



