210 STUDY OF PIG EMBRYOS. 



which for convenience we may term the jugular, — although the application of this 

 name to the vein in its present condition is somewhat inexact, — is cut several 

 times, owing to its irregular course. Its main stem, Jug"" , arises nearly verti- 

 cally through the cervical region and is, relatively to the size of the embryo, of 

 huge diameter. It continues upward, Jug'" , along the dorsal side of the vagus 

 to about half-way between the ganglion nodosum and ganglion jugulare. At that 

 point the vessel curves inward and forward, and, therefore, is not encountered 

 again in this section until, having bent upward again, it shows, Jug' , on its way 

 past the trigeminal ganglion. A branch of the jugular is cut just above the gan- 

 glion, Jug" , and another small and probably not very important branch is shown 

 at Ve. 



The nerves are shown as follows : The optic nerve, N. op, still has its central 

 cavity, which, nearer the median plane, opens into the third ventricle of the brain, 

 and in the section resembles in shape an inverted U. On the side of the nerve 

 toward the mouth there is a deep notch, — the section of the choroid fissure. The 

 trigeminal ganglion, G. tri, is very large, and its trilobate form is clearly indi- 

 cated by the figure. The lobe to which the reference line, G. tri, runs gives off 

 the ramus ophthalmicus ; the lobe nearest the jugular gives off the ramus maxil- 

 laris inferior, while the middle lobe gives off the ramus maxillaris superior. From 

 the ganglion the fibers and nerve-cells extend upward to form the root, N. 5, 

 which joins the hind-brain at a characteristic point, — namely, at the summit of 

 the Varolian bend and where the hind-brain is widest (compare Figs. 113 and 1 25). 

 By its great size and by its topographical association with the lateral apex of 

 the recessus lateralis of the fourth ventricle, the trigeminal ganglion may always 

 be readily identified in sections of embryos. The acustico-facial ganglia, Ac. F, 

 may also be readily determined by their typical position immediately in front of 

 the otocyst, Ot. But it is quite difficult to identify the four components of this 

 complex structure, — namely, i°, the motor root of the facial nerve; 2°, the facial 

 or geniculate ganglion ; 3 , the vestibular ganglion ; 4 , the cochlear ganglion. In 

 figure 124 three divisions are shown. The large, darkly stained division, to 

 which the reference line, Ac. F, runs, and which lies nearest to the otocyst, is 

 the vestibular portion of the acoustic ganglion; the small, light area occupying 

 a middle position in the inferior part of the complex is the motor division of the 

 seventh nerve, or lateral root of the facial ; it can be followed to the brain, which 

 it enters as four bundles of fibers; its path of entrance is shown better in frontal 

 sections (Fig. 1 26, t.m). Just in front of the facial motor root lies a second smaller 

 dark mass, the geniculate ganglion of the facial, with an upward prolongation, 

 the sensory root. The ninth or glossopharyngeal nerve is represented by the gan- 

 glion petrosum, G. petr, and its ascending sensory root. This nerve may be 



