326 F. H. EDGEWORTH 



A tabular statement of the synonyms of the names employed 

 has also been appended. 



Occipital Myotomes and Nerves. Fiirbringer 

 (1897) stated that, in the adult stage of Ceratodus, there are 

 two or three occipital and two occipito-spinal nerves. 



The Plexus cervicalis is formed from x, y, z, or y, z. Sewertzoff 

 (1902) stated that in a 15-7 mm. embryo there are five occipital 

 myotomes in front of the first vertebral arch, the first two being 

 in process of reduction. There are ventral spinal roots corre- 

 sponding to the fourth and fifth. He identified the fourth 

 myotome with x of Fiirbringer, so that the first five are u, v, 

 w, X, y. 



Greil (1918) stated that no vertebral arches are present in 

 a 15-7 mm. embryo, and that they are developed in a 17-8 mm. 

 embryo. Five occipital myotomes are present in front of the 

 first vertebral arch in the latter stage. The first two have 

 no corresponding nerve-roots, the third has a (variable) 

 ventral root, the fourth a ventral root, and the fifth a ventral 

 and a (variable) dorsal root. The Nervus hypobranchialis 

 (which = the Plexus cervicalis of Fiirbringer) is formed from 

 the variable third, and the fourth and fifth nerve-roots. He 

 identified these five myotomes with v, w, x, y, z of Fiirbringer's 

 terminology. 



On comparison of these statements it would appear that 

 (1) Sewertzoff's 15-7 mm. embryo was a little more advanced 

 in development than Greil's 17-8 mm. embryo — vide infra. 

 The embryos I have examined at these stages agree with 

 those of Greil, so that, in all probability, Sewertzoff's embryo 

 was somewhat shrunken. (2) Sewertzoff regarded the fourth 

 myotome — counting from before backward — and Greil the 



