xxviii EXPLANATION OF PLATE 1 8. 



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. i. Section through the hinder part of the medulla oblongata, stage between 

 K and L. Zeiss A, ocul. . 



It shews (i) the vagus commissure with branches on one side from the medulla : 

 (a) 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. o th). 



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. i. 



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 glosso- 

 pharyngeal 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 (r) the rudimentary processus falciformis (pfal] giving origin to 

 the vitreous humour; and (2) the hyaloid membrane (hy m) which is seen to adhere 

 to the retina, and not to the vitreous humour or processus falciformis. 



EXPLANATION OF PLATE 18. (X. p. 44 6.) 

 COMPLETE LIST OF REFERENCE LETTERS. 



Nervous System. 



a r. Anterior root of spinal nerve, n c. Neural canal. / r. Posterior root of 

 spinal nerve, sp n. Spinal nerve, syg. Sympathetic ganglion. 



Alimentary Canal. 



al. Alimentary canal, al v. Caudal vesicle of the postanal gut. d al. Cloacal 

 section of alimentoiy canal, du. Duodenum, hpd. Ductus choledochus. pan. 

 pancreas, sou. Solid oesophagus, spv. Intestine with rudiment of spiral valve. 

 ttmc. Umbilical canal. 



