i66 Journal of Comparative Neurology. 



the ophthalamic which becomes smaller and loses itself near the 

 meso-cephalic aspect of the eye. The oculo-motor terminates 

 near disperse clusters of indifferent (muscle) cells caudad of the 

 eye an lag. 



In E. II the oculo-motor nerve was not recognized, though 

 probably about forming. 



In E. II the relation of the various clefts of the visceral 

 region is especially well shown. The hypophysis is a simple 

 pouch-like diverticle and is in communication cephalad with the 

 mouth cleft and caudad with the eustachian tubes diverticles of 

 the second branchial cleft. These have already begun to assume 

 a tubular form. The preceding clefts are imperforate, the second 

 being represented by ectodermal and entodermal pouches which 

 do not meet, 



Neuromers in the Ophidian Embryo. Waters has given 

 a brief summary of the history of opinion respecting the expan- 

 sions of the medullary tube which have been noticed by most 

 embryologists since VonBaer.^ To this paper the reader is re- 

 ferred for bibliography. 



Balfour recognized the possibility that these "earlier con- 

 strictions may potentially correspond to so many nerve roots. 



Beraneck- in several papers attributes segmental value to 

 these dilations, as did Kuppfer. 



Orr, in studying these expansions, decides (i) that succes- 

 sive neuromers are separated by external dorsoventral internal 

 ridges, (2) that the neuromeric constrictions are symmetrical and 

 opposite, (3) that there is a radial arrangement of cells within 

 each neuromer, (4) that the cells are confined to their respective 

 neuromers, there being a shape line of demarkation, (5) that the 

 nerve roots arise from the crests of each neuromer. The first 

 [hind brain] neuromer gives off the trigemenal, the second the 

 abducens, the third the seventh and eighth, etc., (6) that the 

 mid-brain is not segmented while the fore-brain has two neurom- 



1. Waters B. H. Primitive segmentation of the Vertebrate 

 Brain. Qiia7ierly Joiirtial of Microscopical Science. June, 1892. 



2. Recherches sur le developpement des nerfs craniaux chez les 

 lezards. Reciieil Zool. Suisse. 1887, and Replis medullaires du Poulet. 

 ibidem. 



