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manner and are distributed to the olfactory membrane. From the 
division (b) two main nerve trunks arise — a large one nearer the me- 
dian plane, and a smaller bifurcated one lying between the former 
and division (a). The olfactory cup is also rather imperfectly divided 
into two parts — a median and a lateral — the fibres from (a) supply 
mainly the nasal membrane of the lateral portion and those from 
division (b) mainly the membrane of the median portion. 
The median nerve (nv), as it approaches the lateral bundles, en- 
larges and passes in front of the division (0), it then passes behind 
the two slender branches of division (a), it divides unequally behind 
these, and the main part of it enters into connection with the largest. 
branch of division (a). The fibres do not anastomose, but commingle 
in a very intimate way, they sub-divide and pass to the nasal epithe- 
lium in close association with those of division (a). 
It should be clearly understood that the two separate and distinct 
brain connections (nv) and (a-+b) exist simultaneously for a long time 
before any olfactory lobe is formed. The two brain connections are 
present in embryos about 13 mm long. In specimens 23 mm long no 
lobe is formed, it is only faintly indicated in specimens 25 mm long 
(Fig. 1), it is small in embryos 28 mm long, in those 38 mm long 
it has attained the dimensions shown in Fig. 2. 
Fig. 3, represents a view nearly on the ventral aspect of the 
brain of an embryo 40 mm long. Qn the left side of the Fig. the 
olfactory cup has been broken away. The two median nerves (nv) 
are seen, as in the former specimen, crossing the fore-brain in front 
of division (b), behind the two slender trunks of a, a winting with 
the large lateral nerve trunk of division (a). On the left side the 
principal blood vessels (vs) are indicated that run around the olfactory 
lobe and pass underneath the median nerve. 
Fig. 4, shows a side view of the same specimen. Especial atten- 
tion is directed to the olfactory lobe (Lob) which is clearly diffe- 
rentiated but is still of small size. 
Fig. 5, is a view from above on the brain of an embryo 47 mm 
long in which the median nerve (nv) shows well on the left side. It 
crosses the lobe and disappears into the tissue surrounding the ol- 
factory cup. On the right side, a dissection has been made to show 
the main branches of the lateral olfactory and the union of the 
median nerve therewith. The lobe (Lob) is now becoming prominent 
and bears on its distal summit the divisions (a) and (6). The 
division (a) has been broken from the lobe in order to show better 
its point of attachment, viz., to the outer or lateral part of the lobe. 
