242 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
divisions of encephalomere III, as may easily be determined by a com- 
parison of his figures with frontal sections of swine embryos. He 
says (p. 188), “Die ventrale Ausbuchtung der zweiten Falte kann man 
also mit vollkommene Sicherheit fiir die beginnende Ponsanlage, und 
ihren oberen Theil für die Cerebellumanlage halten.” But, as may be 
determined by the relations of the neuromeres to the ear capsule and to 
the ganglia of the acustico-facialis and the trigeminus in his figures 
(Taf. X. Figs. 4, 5), the true Anlage of the cerebellum lies anterior to 
this and is his “erste Falte,” which on theoretical grounds he considers 
related to the trochlearis nerve. As a result of this mistake it happens 
that the neuromere which he calls “ Abducensneuromer” (VI), and to 
which on purely theoretical grounds’ he assigns the sixth nerve, is in 
reality encephalomere V, which is connected with the acustico-facialis. 
With this neuromere the abducens never is connected in any Vertebrate yet 
studied, In the swine, as I am able to affirm from my own observations, 
the abducens arises from the ventral portion of hindbrain neuromere VI, 
which in the early stages of all Vertebrates lies opposite the ear capsule. 
In Necturus, the chick, and S. acanthias, its origin is ventral and poste- 
rior to the origin of the acustico-facialis. In support of this theory of 
the mechanical origin of the “Falten,” Broman finds that, as a result, 
as he thinks, of the flexure of the neural tube, those neuromeres which 
correspond with encephalomeres IV and VI of my figures are wedge- 
shaped, and that their ventral edges do not reach the ventral wall of the 
neural tube. Moreover, none of his nenromeres extend to the “ Deck- 
platte.” But a study of swine embryos leads me to conclude that this 
is not characteristic of all mammalian embryos, and indeed that it may 
be “ein blosser Zufall” in the case of Broman’s human embryo. In 
young swine embryos (killed 19 days after coitus) none of the neuromeres 
are wedge-shaped ventrally or dorsally ; moreover, the constrictions be- 
tween them extend into the Deckplatte. The posterior constriction 
of encephalomere V extends across the Deckplatte until a somewhat 
later stage, and in this constriction a mass of neural-crest cells persists 
in a way precisely similar to that in which neural-crest cells in S. acan- 
thias persist in the regions of constriction between the primary brain 
vesicles (encephalomeres).* 
From an examination of the evidence presented by those who have 
held that the neuromeres are purely the result of mechanical influences, 
1 In connection with this fact, it is to be noted that the walls of the medulla in 
this region are little distended laterally, which may be ascribed to the influence of 
the ear capsule. (See Plate 5, Fig. 30.) 
