I SENSE ORGANS OP AMIUKUP. 359 1 



The Vagus Group. — This group of nerves escapes from the brain, 

 in two parts (Fig. 15, PI. 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. (R. 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. IX.~) The rest of 

 the vagus group, formed of the whole of the posterior part (Vag. II.) 

 as well as of the greater portion of the anterior part ( Vag. I.) 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 1st 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 imparls. 



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 corn,- 

 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, PI. IV.) In other re- 

 spects the architecture is wonderfully alike. The ventral bundles of 

 longitudinal fibres are subdivided on each side into two compartments 



