Proceedings of the section of sciences - DWC - KNAW

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part of tbe nucleus a position above the aqueduct is possible. Here,
th el'efore , the cells reach to the medialline without, howevel', fOl'ming
Fig. 17. Ciconia alba.
tbe characteristic medial nucleus as in bydl'osaurii and selachii. The
ceU form is l'ound and vesicular. It is difftcuH to judge of the exit
of the fibres. Some can be seen going fl'om the radix to the motor
V nucleus; how the others reach the periphery cannot be stated
with certainty from the normal preparations (ciconia, chrysomitis).
]fammals. Without entering into details regal'ding each order
examined sepal'ately, the most strlking points of resemblance anel
difference may be given here. The distinction made by CAJAL (1. c.)
into nucleus infao-posterior and nucl. supero-anteriol' witbin tbe
boundaries of the mesene. V nucleus can be kept fol' many of tbe
mammais, especially for l'odentia, which have been principally examined
by OAJAL (rabbit, rat). For the two lowest orders of mammals
(monotremata and marsupialia) this distinction does not hold good.
The part of the nucleus, situated in other mammalia (mono delphia)
distally from the mid-brain, is entirely wanting in didelphict or nearly
sa. [n Echidna hystrix srarcely a single mesenc. V cell is to be found
laterally to the aqueduct, still less in the reg ion of the 4 th ventl'icle.
A few have shifted somewhat fl'Om the middle line, dOl'sally to the
aq. Sylvii, the large mttjoriiy lie in every cross plane on the medial
line; (cf. fig. 18, plane of the trochlear nncleus). The nucleus is
exhausted befOl'e the decussation of the nervi trochleal'es .
.J..11arsupialia show similar conditions although a very few ceUs
have come to lie already latel'ûUy to the most rostral pa,d of the
4 th ventriele ; in 1JWC1'OPUS tbis is cleal'er than in clidelphys.
In the case of the last-mentioned animal the nuclei situated dol'sally
on both sides distinctly combine to a single one near the medial
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