278 G. E. COGHILL 



and glossopharyngeal ganglia enter the brain, but the vagus 

 ganglion has no root. The optic cup has deepened greatly and 

 the lens projects deeply into its cavity. The invagination of the 

 olfactory epithelium is more marked but there is not yet an 

 olfactory nerve. 



C. THE COILED-REACTION STAGE 



The disti-ibution of the trigeminal fibers to the skin is much 

 more obvious than in the earlier stage, the mesial terminal branch 

 of the r. ophthahnicus profundus being well defined. A descend- 

 ing trigeminal tract of a composite nature extends to the spinal 

 levels (figs. 3, 5). The giant ganglion cell component of the 

 trigeminus is now particularly clear (figs. 34 to 37). The outline 

 of the jugular ganglion is still indefinite and no perceptible fibers 

 leave the ganglion. The lateral line primordia have become 

 much extended and a mandibular line makes its appearance. 

 Lateral line nerves follow along the primordia closely attached 

 to the skin, although no fibers have been traced in this stage to 

 the mandibular line. All of the lateral line roots form ascending 

 and descending tracts in the brain, and the auditory root forms a 

 short descending tract (fig. 5). The auditory vesicle of this 

 stage is illustrated in figure 77. The geniculate ganglion is still 

 united with its epibranchial placode, but from it emerge several 

 fibers which project ventrad behind the spiracular pouch as an 

 incipient r. alveolaris. The root fibers from this ganglion form 

 the fasciculus solitarius which runs caudad immediately beneath 

 the external limiting membrane to the level of the glossopha- 

 ryngeal root which enters it. Peripherally the glossopharyngeal 

 ganglion connects with its epibranchial placode. The vagus 

 ganglion now has a small root which joins the fasciculus solitarius. 

 Distally this ganglion connects with the ej^ibranchial placodes, 

 but gives rise to no peripheral fibers. The condition of the eye 

 is shown in figure 76. The olfactory epithelium is now in close 

 contact with the brain, but olfactor}^ root fibers do not certainly 

 enter the brain in this stage. 



