280 
The fibres of division (a) are also distributed to the lateral part of 
the olfactory cup, and those from division (6) to the median part. 
Fig. 6, shows a side view of the brain of an embryo 55 mm long. 
The overlying tissue has been dissected away from the base of the 
a ER 
Fig. 6. > about 12 diameters. 
olfactory cup exposing the nerve trunks. The median nerve (nv) is 
shown to take the same course as in former specimens and to unite 
with the largest branch of division (a). 
Fig. 7, shows the brain of an embryo 68 mm long viewed from 
above. A shallow furrow divides the fore-brain into right and left 
hemispheres. The two median nerves (nv) are well shown. Their 
central ends penetrate the brain wall near the median plane. On the 
left side the nerve, after partly crossing the lobe disappears in the 
tissue at the base of the olfactory cup. On the right side both the 
median and the lateral nerves have been dissected out to show the 
relation of their main branches. This is a good stage to show the 
essential features of the olfactory apparatus, just before the extensive 
modifications have set in which greatly change the appearance and 
have led to confusion in appreciating the relationship of the parts 
of the olfactory organ. There is at this stage a medium development 
of all parts. The lobes are well differentiated but as yet there is no 
trace of a tractus and bulb. The branches of the main olfactory, 
separated into two groups (a+b), are borne on the distal surface of 
the lobe and the median nerve (nv) is seen to cross the lobe and to 
unite mainly with the largest branch of group (a). The fibres from (a) 
