260 
The further development of the anterior band of cells shows it 
also to be a complex of two nerves, for its attachment to the brain 
divides into a posterior and an anterior root, the former, running for- 
wards from the depression between the mid-brain and the primary 
fore-brain, meets the latter as it passes backwards from the lateral 
margin of the neuropore, and united they extend down the side of 
the brain posterior to the optic vesicle (fig. 12 th and I). 
Fig. 11. 
Fig. 11. Sagittal section showing the relation of the primary olfactorius to the an- 
terior head cavity a. ect ectoderm. V trigeminus. JV trochlearis. c. g. ciliary ganglion. 
J olfactorius. m nasal epithelium. opt optic vesicle. «a anterior head cavity. 2 mandi- 
bular cavity. 
Fig. i2. Sagittal section through the Anlagen of the anterior cranial nerves. 
J olfactorius. th ,,thalamicus“‘. JV trochlearis. V trigeminus. VIJ facialis. aud audi- 
tory vesicle. meur neuromeres. Dr brain. opt optic vesicle. c. g. ciliary ganglion. 
2 mandibular cavity. 
In my former paper I called the posterior of these nerves the 
»thalamic‘, because of its origin between the thalamencephalon and the 
mesencephalon. The anterior root is the primary Anlage of the ol- 
factorius. This branch of the anterior nerve complex takes its origin 
in a large mass of ganglion cells which are proliferated from the margin 
of the neuropore (fig. 8 Z), and which fuse laterally with the thickened 
ectoderm that, at either side of the neuropore, forms the Anlage of 
the nasal epithelium. Later the primary attachment to the brain is 
lost, and a secondary connection between the brain and the fused 
ectodermic and ganglionic cells is acquired. The olfactorius thus con- 
forming to the type for sensory nerves. 
The „thalamic“ nerve bears no ganglionic enlargement other than 
the ciliary ganglion to which it passes after uniting with the primitive 
olfactorius. I am therefore inclined to think the ciliary ganglion the 
proper ganglion of this nerve. 
