REGIONAL ANALYSIS 53 



The ventral sector of the anterior olfactory nucleus is interpolated 

 between the olfactory bulb and the corpus striatum, as in Necturus 

 (figs. 6, 86). This is the primordium of the tuberculum olfactorium 

 ('27, p. 290), which is enormously enlarged in the lungfishes (Rude- 

 beck, '45). Posteriorly of this nucleus is a poorly defined field, which 

 embraces the ventral angle of the lateral ventricle and is regarded as 

 the probable precursor of the head of the caudate nucleus (fig. 99) 

 It is intimately connected with the rest of the striatum and the 

 septum. The chief efferent path is the olfacto-peduncular tract to the 

 dorsal hypothalamus, ventral border of the peduncle, and inter- 

 peduncular nucleus. 



The middle sector of this complex is the undifferentiated pri- 

 mordium of the mammalian lentiform nucleus, as shown by its 

 fibrous connections. It is characterized by very dense, sharply cir- 

 cumscribed neuropil in the white substance (p. 96; figs. 98, 99, 108, 

 109) and has the typical striatal connections with the overlying pal- 

 lium and the thalamus, including a small sensory projection tract 

 from the dorsal thalamus (fig. 15, tr.th.f.). The chief efferent path is 

 the lateral forebrain bundle (f. lateralis telencephali, /.Za^./.), which 

 contains strio-thalamic, strio-peduncular, and strio-tegmental fibers 

 comparable with the corresponding components of the mammalian 

 extrapyramidal system. There is also a strio-tectal and strio-pretectal 

 connection (figs. 11, 14, 101). The separation of the lentiform nucleus 

 into globus pallidus and putamen is incipient (p. 97). 



15. SEPTUM 



The septum complex occupies the ventromedial wall of the hemi- 

 sphere between the anterior olfactory nucleus and the lamina ter- 

 minalis and hippocampal area (figs. 4, 98, 99) . Its position and con- 

 nections are similar to those of mammals. It is directly connected 

 with the olfactory organ by the nervus terminalis, and it receives 

 fibers from the olfactory bulb, anterior olfactory nucleus, pallium, 

 and hypothalamus. The chief efferent paths are by the medial fore- 

 brain bundle (f . medialis telencephali, f.med.t.) and to the overlying 

 pallium by the f. olfactorius septi ('27, p. 291). There is also a broad 

 connection across the ventral aspect of the hemisphere with the 

 amygdala and the piriform area, the diagonal band of Broca (figs. 96, 

 97, 98, d.b.), and a connection with the habenula by tr. olfacto- 

 habenularis anterior and tr. septo-habenularis (chap, xviii). 



