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Anlagen, somites and visceral clefts. The cells of the ganglionic Anlage of the glosso- 
pharyngeus have been crowded backward by the auditory invagination. 
I— VII, encephalomeres ; a, ‘‘anteriors” (PLATT’s) cavity; 1—7, van WIJHE’s somites; 
sac. vse. 1, sac, vse, 2, sac. vse. 3, visceral ponches 1, 2 and 3; gn. acs-fac., Anlage of 
the acustico-facialis; gn. gls., Anlage of the glossopharyngeus; gn. trg., Anlage of the 
trigeminus; gn. vag., Anlage of the vagus; n’po., neuropore; *, posterior boundary of audi- 
tory invagination, 
stated at length by van WısHE (82) and Horrmann (94). The 
relations as shown in a parasagittal section of an embryo with 
18—19 post otic somites are given in Figure 1; and as seen in an 
embryo with 28 somites, in Figure 6. With Horrmann (94), I am 
able to confirm the presence of the anterior (PLaTtT’s) cavity. If the 
latter be a true somite’), then there exists anterior to VAN WIJHE’S 
6th somite one somite corresponding to each encephalomere; I assume 
that somites and encephalomeres primitively alternated in position, as 
do the myelomeres and trunk somites. Miss PLATT (94) has confirmed 
the presence of VAN WIJHE’s somites in Necturus, and has stated 
that in the hindbrain region neuromeres and somites alternate. 
5. Relations of Neuromeres to Nerves. 
I accept VAN WIJHE’S conception of the primitive segmental 
nerve. This is composed of two roots; one is the dorsal mixed root, 
the sensory fibres of which innervate the skin of each segment, and 
the motor fibres of which supply the musculature derived from the 
lateral plates (splanchnic musculature); the other is the ventral motor 
root, the fibres of which supply the musculature of the somites 
(somatic musculature). The primitive dorsal root was intersomitic, 
and the ventral root somitic, in position (see HATSCHER ’92). The 
dorsal roots are connected with the somite posterior to the myosepta 
in which they lie. From our present knowledge I believe we are able 
to say that the chief distinction between cranial and spinal nerves 
consists in the fact that the ganglia of cranial nerves receive cellular 
material from the skin of the lateral surface of the head, whereas 
the spinal nerves do not. 
Because of the well known shifting of the point of exit of nerve 
roots, motor as well as sensory, it is necessary to take into con- 
sideration in dealing with nerves not only their peripheral distri- 
1) If we should finally come to accept Kuprrer’s (94) view that the 
three anterior cavities (“anterior’, premandibular and mandibular) are 
aborted gill pouches, these cavities would nevertheless offer evidence of 
three segments. 
