809 



III. Description of the sections. ') 



a. Connections of the olfactory nerves. 



As already mentioned tlie olfactory bnlbs and lobes are conspi- 

 cuous strnctnres liiiaterally represented. The most, frontal sections 

 show a bulbar formation which is arranged in a circular manner 

 (Fig. Ill) though no extension of the ventricle (rhinocoele) is visible 

 in this region '). The tila olfactoria, glomeruli and mitral cells are 

 of the usual structure (cf. Edinger, Wallenberg, Holmks, 1903, p. 

 403) and call for no special description. The two separate formations 

 right and left, are distinctly seen throughout (Fig. Ill and IV). Turner 

 (1891, p. 43) and S. P. Gage (1893, p. 197) refer to the degree of 



TrOli 



F>% 



Fio.lV 



diminution in importance of the olfactory connexions in Aves, 

 culminating in the concresence of two small lobes in some higher 

 foinis, as an index of the stage of organisation attained by the 

 brain. The /obus olfactorins is spread out u|)on tiie venti'al aspect 

 of the anterior part of the cerebral hemisphere and is crescentic in 

 cross section (Fig. IV). The second relay olfactory tibres form a distinct 

 tract in the most dorsal lamina of this structure immediately ventral 

 to a small forward prolongation of the lateral ventricle which 

 becomes visible in this region (Fig. IV). These fibres end in the 

 corte.i' /obi o/factorii or area praepirifonnis of Bhodmann (cf. Rose, 

 1914, p. 338). The position of this area immediately dorsal and 

 medial to this ventiiciilar extension can be located in the sections 

 (Fig. IV), though its cell structure is not clearly distinguishable (cf. 

 RosK, op. cit. p. 339, Taf. Ill Fig. 8, 9, 61, Taf. 1, Fig. 13). 



Dorsal and caudal to the area praepiriformis the frontal portion 

 of the septum is an extremely ihin double lamina. (It is shown 

 .somewhat crumpled in the diagrams; cf. Fig. V). Somewhat more 

 caudally frontal to and in the region of the anterior commissure 



1) The sections corresponding to the figures are as follows: ill, 21; IV, 58; 

 V, 179; VI, 204; VII, 21)8; VUi, 212; IX, 235; X, 245; XI, 262; Xil, 283 

 XIII, 293; XIV, 3U3. 



-■) For the lettering used in the figures see pages 822 and 823. 



53 



Proceedings Royal Acad. Amsterdam. Vol. XXVI. 



