228 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The glossopharyngeus is now in fibrillar connection with the lateral 
walls of the neural tube at a point behind encephalomere VII. ‘The 
fibres from the ganglion cells of the vagus enter the neural tube at a 
point somewhat behind the point of origin of the glossopharyngeus. 
The cells of the two nerve Anlagen, however, still appear continuous. 
Posteriorly, and at the same level as the origin of the roots of nerves IX 
and X, the neural-crest cells appear as a commissure (coms. d.) con- 
necting the vagus Anlage with the ganglia of the dorsal spinal nerves 
Ventrally the vagus divides into four mixed (post trematic) branches, 
each of which innervates the skin and musculature of a visceral arch, 
and posteriorly is continued beneath the skin as the ramus lateralis 
vagi along the medio-lateral line.! 
At this stage, I find the first evidence of the olfactory nerve (I) in 
the form of connecting strands or fibres between the anterior lateral wall 
of the forebrain (prosencephalon) and the thickened lateral epithelium 
of the olfactory plate. The connection between the median portion of 
the “Riechplatte” and the brain wall (neuropore) has disappeared at a 
somewhat earlier period (8-9 mm.). According to Marshall (’78) and 
Beard (’85) the olfactory nerve develops, as do the other dorsal cranial 
nerves, from cells of the neural crest, and is therefore regarded by them as 
a nerve morphologically comparable with the dorsal cranial nerves. The 
evidence given by van Wijhe (86°) and Hoffmann (96), however, serves 
in the opinion of these investigators to render this view improbable. 
Van Wijhe (86°, p. 680) states that “das Riechorgan und der Nerv ent- 
stehen beide aus dem vorderen Neuroporus. Der Olfactorius entwick- 
elt sich nicht aus der Nervenleiste, denn er tritt in einer Periode auf, 
wann dieselbe im Kopfe schon lángst geschwunden ist; auch ist er von 
Anfang an mit der Haut in Verbindung und unterschéidet sich durch 
diese zwei Merkmale von allen übrigen dorsalen Nervenwurzeln. Der 
Riechnerv entsteht also erst nach dem Acranienstadium und in Ueberein- 
stimmung damit ist seine Abwesenheit beim Amphioxus.” 
Confirmatory of this view is the evidence given by Hoffmann (’96, 
p. 272) that “der Riechnerv fehlt [in Squalus] aber bis zu diesem Ent- 
wicklungsstadium [10-12 mm.] noch vollständig und erst bei Embryo- 
nen, welche eine Länge von 134-14 mm. erreicht haben, beginnt er sich 
anzulegen. Bis zu dieser Periode liegt die Riechgrube der Medullar- 
1 Squalus possesses no dorso-lateral line nerve corresponding with that of 
Cyclostomata, Dipnoi, and Ganoidei. I also find no evidence in Squalus such as 
that found by Miss Platt (’94) in Necturus, to show that there once existed a ventro- 
lateral line in Vertebrates. 
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