156 



C. Judson Herrick 



foramen is a very sharply circumscribed área which is regarded as 

 primordial corpus striatum (figs. 8, 9, lO). It extends laterally for a 

 short distance into the evaginated hemisphere. This área seems te be 

 comparable with the área somática oí Acipenser, for it receives fibers 



from the área dorsalis and discharges 

 into the thalamus. The latter path is 

 the tractus strio-thalamicus or soma- 

 tic projection tract, which may con- 

 tain ascending fibers also, though these 

 have not been described. Behind the 

 foramen and extending also laterally a 

 short distance into the hemisphere is a 

 ventricular eminence termed by He- 

 rrick and Obenchain lobus subhippo- 

 campalis, which is structurally very 

 distinct from both the «striatum» be- 

 low and the área olfactoria dorsalis 

 above (figs. 8, lOj. Nothing is known 

 regarding its fibrous connections, but 

 its relations to the other parts of the 

 telencephalon médium and thalamus 

 suggest very strongly that it and the 

 «striatum» together are comparable 

 with the área olfacto-somatica and área 

 somática of Acipenser. This seems 

 also to be Johnston's opinión (cf. the 

 schema, fig. 40, p. 403, of his 1912 

 paper). 



Summary. — In Petromyzon the 

 evagination of the rostral end of the 

 telencephalon has progressed beyond the stage represented by Acipen- 

 ser, for a part of the área olfactoria is joined with the bulbus olfactorius 

 in the formation of the cerebral hemisphere. The residue of the telen- 

 cephalon, however, exhibits some arrangements which are probably more 

 primitive. The walls of the telencephalon médium are subdivided into 

 three longitudinal zones whose topographic arrangements (fig. Il) are 

 closely similar to those of Acipenser (fig. 6j. They converge in front 



nuc. posto, 

 hyíhr 



Fig. 10. — Trans verse section from 

 the same series as the last immedia- 

 tely behind the foramen, illustrating 

 the área olfactoria dorsalis (marked 

 fr/m. hip.), área olfactoria lateralis 

 (1. ol.), lobus subhippocampalis (1. 

 s/ij>.), and Corpus striatum (c. s.). 



i 



