No. 408.] STUDY OF MAMMALIAN EMBRYOLOGY. 939 
fibre tract, which is oval in section, lies just below the enter- 
ing vestibular fibres, and is indicated in the engraving ; finally, 
the motor tract (¢7.) of the facial; this tract is a very distinctly 
marked bundle of nerve fibres, which traverse the ventral zone 
of the medulla almost horizontally, then come downwards and, 
passing out from the brain-wall, form the /azera/ root of the 
facial; this root runs 
first towards and then £/.~ 
past the geniculate gan- 
glion. The jugular vein 
(Jug. lies outside the — "* 
ganglia, not inside, as 
in Fig. 9. In the man- 
dibleappeartwonerves; Ss. 
of these the upper is the 
hypoglossal (JV.xzz.); 
lies near the angle "&- 
formed by the junc- “acm. 
tion of the first gill- 
cleft with the pharynx 
proper ; the lower is the 
inferior maxillary. Ph. 
The next figure is 
from a section not far GE 
from the last and chosen 
to show the otocyst "jg uereneyi Cok, cules Da, but culo 
The hind-brain has nar- lymphaticus ; mp €— Fac.m., motor division of 
: the poe nerve; Jug., jugular; Md.obl., medulla oblon- 
rowed considerably ; its gata; P. , Macias RUE. tall Ape dla adi 
thickened floor ( Md. d "Ii PUER sings of the semicircular canals; Ve., 
ob/.), the anlage of the 
medulla oblongata, rises steeply from the median line; its 
ependymal roof (Z/.) is less expanded than in Figs. 9 and 10 
and forms a sharp angle in the dorsal median line. The 
two sides of the medulla are separated by a deep fissure 
(cf. Fig. 10, f.), underneath which the wall of the brain is corre- 
spondingly thinned, constituting the floor plate (Ap/.), which 
is transformed in the adult into the median raphe. The 
pharynx (Z/.) is wide and is expanded laterally into the common 
Ma.obl. 
Coch, - 4t 
