42 NERVOUS SYSTEM OF VERTEBRATES. 



ular portion, and a lower cochlear portion. 9, glossopharyngeal with its superior 

 ganglion, s, above; its petrosal ganglion, p, below; and its three branches, — iy., 

 tympanic; /. r., Ungual ramus; ph. r., pharyngeal ramus. 10, vagus, with its jugular 

 ganglion, j, extending posteriorly as a ganglionic commissure, com.; and below, its 

 ganglion nodosum, n. Its branches form the laryngeal plexus, beyond which is 

 the recurrent nerve, rec. Just below the jugular ganglion is the auricular branch 

 of the vagus. II, accessory, which joins the vagus; ex., its ramus externus. 

 12, hypoglossal. F., Froriep's hypoglossal ganglion. C. I, C. 2, C. 3, cervical 

 nerves. 



Brain and Sense Organs. Telen., telencephalon. Dien., diencephalon. Mesen.,. 

 mesencephalon. Meten., metencephalon. Myeleit., myelencephalon. H., hem- 

 isphere. Vcn. IV., roof of the fourth ventricle. Op., optic cup. L.lens. Na., nasal 

 pit. Ot., otocyst. 



ward in relation to the spinal cord. Farther forward a sharper 

 flexure in the opposite direction is found, called the pontial flexure, 

 because the pons of higher vertebrates appears at this point. 

 Then the front end of the brain is curved down again in such a 

 way as to bring the ventral surface of the brain just behind the 



/ Eye 



Fig. 21. — Transverse sections through the region of the optic vesicles in selach- 

 ian, avian and mammalian embryos : A, Torpedo ocellala ; B, Gallus domeslicus ; 

 C, Cavia cobaya. After Froriep. These and the following figure show that the 

 optic vesicles arise from the borders of the neural plate. 



closed neuropore nearly into contact with the pontial flexure. 

 The last bend, from its position in the parietal region of the head, 

 is called the parietal flexure. It corresponds in position to the 

 future mesencephalon. These flexures are in themselves of no 



