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cells uniting the anterior portion of the mandibular cavities with the 
dorsal wall of the alimentary canal. 
c) That part of the alimentary canal which lies in front of the 
infundibulum gives rise to the anterior pair of head cavities. They 
are followed by the praemandibular cavities arising in tissue pro- 
liferated from the dorsal wall of the alimentary canal. The mandibular 
cavity arises from the fusion of two cavities, each apparently the 
homologue of a somite. Three mesodermic somites lie above the 
hyoid arch. 
d) A nerve complex arises from the neural crest, anterior to the 
trigeminal and trochlear Anlagen. It gives rise to the primitive 
olfactorius and to a posterior nerve, which I have called the ,,thala- 
micus“ from its origin between mesencephalon and thalamencephalon. 
This nerve is probably the primitive or dorsal root of the oculo- 
motorius. 
e) Cells extending from the common neural Anlage of the ,,tha- 
lamic“ and olfactory nerves unite with the walls of the „anterior“ 
and of the praemandibular cavities. Muscle cells are later developed 
in the walls of both pairs of cavities. We have therefore both sensory 
and motor elements of two head segments anterior to the mandibular 
cavities. 
f) Both anterior and posterior to the infundibulum a fusion takes 
place between the ectoderm and the median ventral cells,. which unite 
on the one hand the „anterior“ head cavities, on the other, the prae- 
mandibular cavities. Inasmuch as these cells arise from the ventral 
wall of the alimentary canal it is possible to interpret the fusion as 
indicatory of the reduction of gill-clefts anterior to the hyo-mandibular. 
g) The above interpretation is favored by the facts: (1), that, 
in Batrachus, pockets from the alimentary canal open to the exterior, 
anterior to the mandibular arch, and in the region of the future 
mouth; (2), that, in Batrachus, cells are proliferated from the ecto- 
derm to meet the lateral margin of the praemandibular cavity. 
h) The mouth involution in Batrachus is double, and at first a 
median partition divides the oral opening. 
Freiburg i. B., March 19./1891. 
