No. 408.] STUDY OF MAMMALIAN EMBRYOLOGY. 937 
nerve, the so-called Ehrenritter’s ganglion, is represented by an 
accumulation of cells in the upper part of this root. As 
regards the tenth nerve, or vagus, both its ganglia and the 
fibrous trunk connecting them are shown. The upper or 
jugular ganglion (G.jug.) is nearly on a level with the otocyst, 
while the lower or nodosal (G.zoZ.) lies near the cervical 
sinus. To the nerve trunk zr. 
between the two ganglia are 
adjoined the fibres of the mes. 
eleventh or spinal accessory 
nerve, which does not other- £4. 
wise appear in this section. A 
small piece only of the hypoglos- 
sal nerve can be seen (Writ). 
The space occupied by this. 7.s. 
nerve is blank in the engraving; Z.R, 
in the specimen it shows hori- 
zontal fibres. £ 
. The frontal series has special 
value for the study of the hind- Jug. 
brain, its nerves, and of the oto- 
cyst. From this series I present 
here three figures of the head 
region. The first of these sec- 
$ - Fic. 9.— Pig of 12.0 mm. Series No. 6. 
tions (Fig. 9) passes through Frontal section 284. Æc., ectoderm; 
the widest part of the hind- Eż., ependymal roof of the fourth ven- 
; tricle; D.Z., upper portion of the do 
brain and through the roots zone of His; G.éz., ganglion trigemini; 
ot the trigeminis: <The pav — e o 
i j x i of the trigeminal nerve; »zes., mesen- 
ity of the hind-brain is dia 7.5, c0 soda, ‘of W. 
His. x22 dia 
enormously distended ; it is 
bounded on the dorsal side only by a very thin wid of cells, 
the epithelial roof or ependyma (Æż.), which does not form 
part of the true nervous structures, although it passes into 
and is directly continuous with the dorsal zone (D.Z.) of the 
medulla oblongata, which is thus seen (also in Figs. 10, 11) 
to be only the thickened ventral wall of the neural tube, just as 
the ependyma is the attenuated dorsal wall. The trigeminal 
ganglion (G.tri.) is very large and sends its sensory fibres 
