THE TELENCEPHALON IN CYCLOSTOMES! 
J. B. JOHNSTON 
From The Institute of Anatomy, University of Minnesota 
FORTY-ONE FIGURES 
The telencephalon of cyclostomes presents in many ways more 
primitive conditions than are known in other vertebrates. Cyclo- 
stomes are therfore important in the effort to trace the phylogeny 
of various structures in the cerebral hemispheres. The discussions 
regarding the interpretation of the lateral lobes, the pallium and 
the ventricles (Ahlborn, Rabl-Riickhard, Studnicka, Edinger) 
together with the contributions by Sterzi (09) and the writer 
(02a), have made clear the significance of most parts of the telen- 
cephalon at least in Petromyzonts. The lateral lobes are true 
hemispheres,? containing lateral ventricles connected with the 
third ventricle by wide interventricular foramina. The hemis- 
pheres are pushed back against the sides of the diencephalon by 
pressure from the buccal apparatus. The bulbar formation occu- 
pies the broad rostral wall of the hemisphere and does not project 
forward as a bulbus olfactorius. In addition to this bulbar forma- 
tion the hemisphere walls include secondary olfactory centers 
. and a basal-central area heretofore known as corpus striatum. 
The bulbar formation and secondary olfactory centers are sepa- 
rated by a groove which represents the olfactory peduncle. 
The anterior portion of the third ventricle is closed above and 
rostrally by a membrane which is thickened in two places by 
commissures (figs. 5. 6). Rostral to the extraordinarily thick 
1 Neurological Studies from the Institute of Anatomy, University of Minnesota, 
No. 16. 
2 The writer here uses the term hemisphere as synonymous with the lateral lobe 
or evagination of the telencephalon, accepting in this the suggestion of Professor 
Herrick (710, p. 492). . 
341 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 4 
AuGusT, 1912 
