Figs. 15a and 15b. Two longitudinal and vertical sections through the head of a Pristiurus embryo belonging to stage K. Zeiss a, ocul. 3.
15a is the most superficial section of the two. It shews the constitution of the seventh and fifth nerves, and of the intestinal branch of the vagus. The anterior branch of the seventh nerve deserves a special notice.
15b mainly illustrates the dorsal commissure of the vagus nerve (com) continuous with the dorsal commissures of the posterior root of the spinal nerves.
Fig. 16. Two longitudinal and vertical sections of the head of a Pristiurus embryo belonging to the end of stage K. Zeiss a, ocul. 1.
16a passes through the median line of the brain and shews the infundibulum, notochord and pituitary body, etc.
The pituitary body still opens into the mouth, though the septum between the mouth and the throat is broken through.
16b is a more superficial section shewing the head-cavities pp 1, 2, 3, and the lower vagus commissure.
[Plate 16]. (X. p. 397.)
Complete List of Reference Letters.
auv. Auditory vesicle. cb. Cerebellum. cer. Cerebral hemispheres. ch. Notochord. cin. Internal carotid. ft. Fasciculi teretes. in. Infundibulum. lv. Lateral ventricle. mb. Mid-brain, or optic lobes. md. Medulla oblongata. mn. Mandible. ol. Olfactory pit. oll. Olfactory lobe. op. Eye. opn. Optic nerve. opth. Optic thalamus. pc. Posterior commissure. pcl. Posterior clinoid. pn. Pineal gland. pt. Pituitary body. rt. Restiform tracts. tv. Tela vasculosa of the roof of the fourth ventricle. iv. v. Fourth ventricle. vii. Seventh nerve. x. Rudiment of septum which will grow backwards and divide the unpaired cerebral rudiment into the two hemispheres.