16 F. L. LANDACRE 
anterior division of the X ganglion. Posterior to this level the 
neural crest gradually becomes narrower dorsoventrally and 
passes into the neural crest of the spinal cord. In referring to 
the V, VII, IX, and X ganglia it is to be understood that only 
the general cutaneous and general visceral portions of these 
ganglia are under consideration. These are homologous to 
spinal ganglia. The special somatic and special visceral ganglia 
are referable to other sources. 
‘The endodermal derivatives at this stage fall into two regions. 
First the posterior head region, which extends cephalad to the 
level of the anterior end of the alimentary canal and is char- 
acterized by the presence of somites and a two-layered lateral 
mesoderm. The somites are not well defined at this stage and 
the lateral mesoderm forms a broad sheet extending from a level 
slightly dorsal to the notochord to the ventral limit of the body, 
being absent only in the heart region and the region of the 
stomodaeum. 
The second, or anterior head region, lies anterior to the level 
of the anterior end of the alimentary canal and forms a loose 
mesial or axial mass of entodermal mesenchyme and two lateral 
extensions. These lateral extensions contain cavities which in 
the urodeles do not form definite head cavities or somites, but 
their dorsal portions are undoubtedly homologous to the head 
somites of selachians. The dorsal border of this entodermal 
mesenchyme maintains the same relative level as the dorsal 
border of the somites. It reaches cephalad to the vertical level 
of the middle of the optic vesicle and ventrally it forms a promi- 
nent extension, which is separated from the anterior border of 
the lateral mesoderm by an area free from mesoderm cells. This 
area’ corresponds roughly to the future position of the spiracular - 
gill cleft. The ventral border of this extension reaches nearly 
to the ventral limit of the optic vesicle. The whole of this 
anterior head mesoderm consists of the large endoderm cells 
containing large yolk granules and except those regions giving 
rise to eye and branchial muscle has a loose arrangement presag- 
ing its modification into typical mesenchyme. The neural crest 
overlaps the cells derived from endoderm at two points only— 
