NERVUS TERMINALIS: TURTLE 



427 



In sections of corresponding stages, cut in the sagittal plane, two 

 or three roots were observed to enter the brain substance, but 

 their fibers could be followed within the brain for only a short 

 distance (fig. 2). 



On following these roots distally from the brain, they are seen 

 to unite (figs. 1 and 2) and a ganglionic swelling was invariably 

 found just beyond their point of union. In the dissection figured 

 it will be noted that the two more dorsal roots unite to form a 

 single short trunk before entering the ganghon, while the ventral 

 root enters the ganghon directly. In sections a number of 

 ganglion cells (figs. 2 and 3) may be observed in this mass, but 

 in none of the embryos examined did this ganglion appear to have 

 as many cells as others located more rostrally, especially the one 

 marked gn. (fig. 3). 



Rostrally from the ganglionic mass which lies at the junction 

 of the rootlets, the nerve continues as a compact trunk as far as 

 the most anterior part of the olfactory bulb, midway between the 



Fig. 1 Dissection of head of turtle embryo of 11-mm. carapace length to 

 show the nervus terminalis and its relation to neighboring structures. The 

 left lateral half of the brain is viewed from the mesial aspect. X ca. 15. 



Fig. 2 Central roots of the nervus terminalis at their point of junction with 

 the brain. Turtle embryo of 11-mm. carapace length. Hematoxylin and 

 orange G stain. X 410. 



Fig. 3 Reconstruction of the right nervus terminalis of turtle embryo of 

 11-mm. carapace length, stained with hematoxylin and orange G. The nervus 

 terminalis is represented as lying on the medial surface of the vomeronasal 

 nerve for all of that part of its course which is parallel to the latter. Fart of 

 its course, however, as shown in figure 1, is lateral to the vomeronasal nerve. 

 X ca. 16. 



ABBREVIATIONS 



hl.v., blood-vessel 



hu.olf., olfactory bulb 



cer.hem., cerebral hemisphere 



cr.cav., cranial cavity 



gn., main ganglionic mass (ganglion 



terminale) of nervus terminalis 

 gn.', accessory ganglion terminale 

 gn.c, ganglion cells 

 gn.cl., ganglionic clusters 

 mes., mesencephalon 

 m.ob.do., dorsal oblique muscle 



m.ob.ven., ventral oblique muscle 



m.r.ant., anterior rectus muscle 



n.olf., olfactory nerve bundles 



n.oph., ophthalmic branch of V nerve 



n.ter., nervus terminalis 



n.vom., nervus vomeronasalis 



na.ant., anterior naris 



na.po., posterior naris 



olf.epith:, area of olfactory epithelium 



op.chi., optic chiasma 



ret., retina 



