vii._a._ Anterior branch of seventh nerve. _ar._ Anterior root of spinal nerve. _auv._ Auditory vesicle. _cer._ Cerebrum. _ch._ Notochord. _ch._ Epithelial layer of choroid membrane. _gl._ Glossopharyngeal nerve. vii._hy._ Hyoid branch of seventh nerve. _hym._ Hyaloid membrane. _ll._ Lateral line. v._mn._ Ramus mandibularis of fifth nerve. vii._mn._ Mandibular (spiracular) branch of seventh nerve. v._mx._ Ramus maxillæ superioris of fifth nerve. _nl._ Nervus lateralis. _ol._ Olfactory pit. _op._ Eye. v._opth._ Ramus ophthalmicus of fifth nerve. _pch._ Parachordal cartilage. _pfal._ Processus falciformis. _pp._ Head cavity. _pr._ Posterior root of spinal nerve. _rt._ Retina. _sp._ Spiracle. v. Fifth nerve. vii. Seventh nerve. _vc._ Visceral cleft. _vg._ Vagus nerve. _vg.br._ Branchial branch of vagus. _vgcom._ Commissure uniting the roots of the vagus, and continuous with commissure uniting the posterior roots of the spinal nerves. _vgr._ Roots of vagus nerves in the brain. _vgin._ Intestinal branch of vagus. _vh._ Vitreous humour. Fig. 1. Diagram of cranial nerves at stage L. A description of the part of this referring to the vagus and glossopharyngeal nerves is given at p. 426. It should be noticed that there are only five strands indicated as springing from the spinal cord to form the vagus and glossopharyngeal nerves. It is however probable that there are even from the first a greater number of strands than this. Fig. 2. Section through the hinder part of the medulla oblongata, stage between K and L. Zeiss A, ocul. 2. It shews (1) the vagus commissure with branches on one side from the medulla: (2) the intestinal branch of the vagus giving off a nerve to the lateral line. Fig. 3. Longitudinal and vertical section through the head of a Scyllium embryo of stage L. Zeiss a, ocul. 2. It shews the course of the anterior branch of the seventh nerve (vii.); especially with relation to the ophthalmic branch of the fifth nerve (v._oth_). Figs. 4_a_ and 4_b_. Two horizontal and longitudinal sections through the head of a Scyllium embryo belonging to stage O. Zeiss a, ocul. 2. 4_a_ is the most dorsal of the two sections, and shews the course of the anterior branch of the seventh nerve above the eye. 4_b_ 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.