148 



C. íudson Herrick 



entire length and at the posterior end is connected with the habenula of 

 the epithalamus by a fiber tract, the stria medullaris (fig. 2). This pro- 

 bably represents the most priniitive diencephaHc connection ot the dorsal 

 área, for, as \ve shall see beyond, the connection with the habenula is 

 more intímate in cyclostomes. 



The nerve cells of the área dorsalis are arranged in a characteristic 

 lamellated pattern and are separated from those of the underlying regions 



st r. med 



com.ant. 

 f.med.t 



a. 01. d. 



Pig. 4.— Diagrammatic transversa section through the telencephalon médium 

 of Acipcnser at the level of the commissura anterior. The outline is based on 

 figure 25, píate b, of Johnston (1901) and the internal structures are drawn in from 

 various other figures b)- the same author. Only the ascending fibers of the tractus 



pallii are drawn. 



by a cell-free zona limitans. The ventro-medial border is generally mark- 

 ed also by a ventricular limiting sulcus. 



The physiological factors operative in the differentiation of the área 

 dorsalis are of diíferent kind from those just described for the área me- 

 dialis. Its non-olfactory fibers enter, not from the adjacent epithalamus, 

 but chiefly from the liypothalamus through the tractus pallii (figs. 2, 4). 

 This is a strong tract of ascending and descending fibers which is present 

 in the brains of all fishes (for the relations of this tract in Acipenser see 

 Johnston, iQlla, p. 5 10). The connection of the área dorsalis with the 

 habenula is largely (perhaps exclusively) efferent. 



The área dorsalis, therefore, like the área medialis, is in reciproca! 

 relation by ascending and descending fibers with the hypothalamus and 



