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9 
to the mid trunk region, but is represented in the 
figure as cut off between the second and third spinal 
ganglia. The dorsal ganglionic commissure (Comm.d.) 
is still continuous between the vagus and the first 
spinal nerve. Two slight enlargements of the com- 
missure represent the first and second occipital ganglia 
respectively. The ventral roots of the spino-occipital 
are seen extending under the cover of the posterior 
part of the vagus ganglion. The first four spinal 
nerves are completely reconstructed;; it will be noticed 
that the second, third and fourth extend backwards 
towards the base of the pectoral fin. In the trunk 
region the dorsal ganglionic commissure is now absent 
except between the thirty-second and thirty-third spinal 
ganglia (Sp.g.). The sympathetic ganglia (Symp.) are 
much enlarged and are present on all the spinal nerves. 
The eye is omitted from this reconstruction, but the 
As in 
the preceding reconstruction the ventral wall of this 
optic stalk is shown in cross section (Op.s.). 
structure is somewhat thickened, indicating the in- 
vasion of the optic fibers. The origin of the olfactory 
nerve is indicated in stipple upon the base of the 
lateral surface of the telencephalic vesicle (N.olf.). 
The terminal nerve, of Pınkus or Locy (N.term.) 
arises just mesial to the olfactory. The otocyst shows 
a considerable advance in development when compared 
with the condition of this structure in the preceding 
embryo, the anterior, lateral, and posterior canal 
pockets (O.p.ant.; lat.; post.) are distinctly outlined and 
the sacculus (Sae.) which was barely indicated in the 
otocyst of the 18 mm. embryo is now a well marked 
sack lying below the lateral canal pocket. The ductus 
endolymphaticus arises from the mesial wall of the 
otocyst. 
As has been mentioned above the pharynx is 
only indicated in outline. From its anterior dorsal 
angle springs the hypophysis (Hyp.) now distinctly 
divided into an anterior expanded portion and a 
narrower posterior stalk. The anterior portion is in 
turn subdivided into one median and two lateral 
pouches. The anterior end of the oesophagus (Oes.) 
is much expanded transversely, but becomes reduced 
almost immediately into a tube which is almost circular 
in cross section. The stomach ($t.) is somewhat dilated 
nn 
