208 THE BRAIN OF THE TIGER SALAMANDER 



figures seem to place it in the region of the anterior commissure be- 

 tween the septum and the preoptic nucleus. The efferent pathway 

 from this center decussates in the vicinity of the interpeduncular 

 nucleus. Further information about the connections and physiologi- 

 cal significance of this center is desirable. 



These experiments yield no crucial evidence of participation of the 

 interpeduncular nucleus in the components of mating behavior under 

 investigation or of movements of the limbs in general. This nucleus 

 may play a more specific part in some other types of behavior; and 

 some experiments indicate that this is true. 



The only direct experimental evidence about the functions of the 

 interpeduncular nucleus of mammals known to me is a recent note 

 by Bailey and Davis ('42a) in which they describe a "syndrome of 

 obstinate progression" in cats following destruction of this nucleus. 

 This is a locomotor impulsion, which continues without remission 

 until the death of the animal. Mettler and Mettler ('41) have pro- 

 duced similar symptoms by lesions involving the head of the caudate 

 nucleus, and more recently Mettler ('45, p. 180) describes in primates 

 a direct connection from the globus pallidus to the interpeduncular 

 nucleus. The caudate is supposed to be one link in a chain of conduc- 

 tors with inhibitory functions (Fulton, '43, p. 456) and the syndrome 

 following the destruction of the interpeduncular nucleus suggests to 

 me that this nucleus also may be an inhibitor. The "obstinate pro- 

 gression" may then be interpreted as a release phenomenon. 



In mammals efferent fibers from the interpeduncular nucleus have 

 been described with distribution to neighboring parts of the brain 

 stem, of which by far the most important is the large pedunculo- 

 tegmental tract to the dorsal tegmental nucleus and the related dor- 

 sal longitudinal fasciculus of Schiitz. In the recent study of this fas- 

 ciculus of the opossum by Thompson ('42), she describes this inter- 

 peduncular connection as an important component of it. In this mar- 

 supial the dorsal longitudinal fasciculus is a complicated system of 

 fibers, chiefly descending, connecting the deeper areas of gray be- 

 tween the diencephalon and the spinal cord. 



The structure and connections of the dorsal longitudinal fasciculus 

 suggest general functions of some sort rather than control of local 

 reflexes. Another series of experiments by Bailey and Davis ('42) 

 shows that this fasciculus has some activating function which is es- 

 sential for maintenance of normal motor behavior. They succeeded 



