7a 
SENSE ORGANS OF AMIURUS, 359) 
The Vagus Group.—This group of nerves escapes from the brain 
in two parts (Fig. 15, Pl. I.), anterior and posterior, vagus I. and 
II. The former is chiefly derived from the anterior planes of the: 
vagus lobes, the latter from the posterior. With the former are 
associated the broad nerve fibres from the tuberculum acusticum 
referred to as the acustic root of the vagus group. (A. ac. vag. I.) 
Certain very slender motor roots, with a pronounced inclination 
backwards, join the two parts of the vagus group from the lower 
surface of the oblongata. One of these alone is connected with the 
glossopharyngeus after its separation from the anterior part, while 
two or three join the posterior part. 
From the anterior part is detached the comparatively slender 
glossopharyngeus nerve, which escapes from the skull by a separate 
small aperture in front of the foramen for the vagus proper, and im- 
mediately expands into a large ganglion trunci (G. LX.) The rest of 
the vagus group, formed of the whole of the posterior part (Vag. JJ.) 
as wellas of the greater portion of the anterior part (Vag. J.) escapes 
through an independent foramen, and then forms the large ganglionic 
complex (G. X.) from which the various branches of the vagus group 
are derived. 
As springing from the oblongata within the cranial cavity may be 
mentioned the Ist spinal nerve, which does so by two distinct roots 
escaping through the occipital region in the same horizontal plane as 
the osseous roof of the cavum sinus imparis. 
Reserving for separate description the course of the cranial nerves 
outside the brain case, I proceed to consider certain points as to the 
structure of the brain, which the diagrams on Plate V. will serve to 
elucidate. 
The section represented in Fig. 1 is through the vagus lobes of the 
oblongata near their posterior border, and in fact through the com- 
missura cerebri infima of Haller. It may be compared with Fig. 22, 
Taf. XVI. of Mayser’s paper, but it will be observed that the vagus 
lobes are not so widely divaricated from each other in Amiurus as in 
Cyprinus. The sensory root of vagus IT. has a direction somewhat 
dorsal as it escapes, so that in horizontal sections of young fish trans- 
verse sections of this part of the root are met with above the level of 
its emergence from the oblongata (Fig. 11, Pl. IV.) In other re- 
spects the architecture is wonderfully alike. The ventral bundles of 
longitudinal fibres are subdivided on each side into two compartments 
