Figs. 4a and 4b. Two horizontal and longitudinal sections through the head of a Scyllium embryo belonging to stage O. Zeiss a, ocul. 2.
4a is the most dorsal of the two sections, and shews the course of the anterior branch of the seventh nerve above the eye.
4b is a slightly more ventral section, and shews the course of the fifth nerve.
Fig. 5. Longitudinal and horizontal section through the hind-brain at stage O, shewing the roots of the vagus and glossopharyngeal nerves in the brain. Zeiss B, ocul. 2.
There appears to be one root in the brain for the glossopharyngeal, and at least six for the vagus. The fibres from the roots divide in many cases into two bundles before leaving the brain. Swellings of the brain towards the interior of the fourth ventricle are in connection with the first five roots of the vagus, and the glossopharyngeal root; and a swelling is also intercalated between the first vagus root and the glossopharyngeal root.
Fig. 6. Horizontal section through a part of the choroid slit at stage P. Zeiss B, ocul. 2.
The figure shews (1) the rudimentary processus falciformis (pfal) giving origin to the vitreous humour; and (2) the hyaloid membrane (hym) which is seen to adhere to the retina, and not to the vitreous humour or processus falciformis.
[269] Ent. d. Unke, p. 304.
[270] Das Gehirn d. Selachier, Leipzig, 1870.
[271] Proceedings of the Zoological Society, 1876, Pt. 1. pp. 30 and 31.