346 CHARLES CLIFFORD MACKLIN 



responding parts of the occipital and first and second spinal 

 vertebrae. 



The paired cartilages of the body of the occipital scleromere 

 of Levi's 14 mm. stage appear to be slow in joining dorsally, 

 being found separated in this region by the perichordal septum, 

 while their ventral parts are united. This is possibly to be ex- 

 plained as a result of expansion in this region, from intracra- 

 nial pressure. 



The above identification of the cartilaginous neural arch of 

 the occipital vertebra and its appendage, the transverse proc- 

 ess, as found in the early Levi models does not agree with this 

 author's own interpretations of his findings. In his earliest 

 human skull, from a 13 mm. embryo, Levi shows, lateral to the 

 roots of the hypoglossal nerve, what he calls the lateral portions, 

 from whose lateral surfaces the Querleisten project directly 

 outward, and he figures the latter in all four of his stages. In 

 the 14 mm. stage he finds in each lateral portion, just external 

 to the hypoglossal nerve roots (Levi, text fig, 2) a cartilaginous 

 center, which speedily joins with that for the body mass, which 

 latter, as has already been noted, represents the chondrification 

 of the body of the occipital scleromere. It seems evident that 

 the center of chondrification in Levi's lateral portion is the 

 center for the neural process of the occipital scleromere, with 

 possibly the addition of the center for the undifferentiated por- 

 tion, and hence it follows that the club-like membranous mass 

 in which this nodule is found is the neural process of the occipital 

 scleromere, which, with its partner, builds the lateral part of 

 the neural canal of the occiput. Furthermore, these lateral por- 

 tions are in direct alignment with the spreading arch-processes 

 of the underlying cervical vertebrae, as is shown by the illus- 

 trations of Levi, and, though this author does not label them as 

 the arches of the occipital vertebra, Bardeen, in his copy of Levi's 

 illustration of his 13 mm. stage in Keibel and Mall's "Human 

 Embryology" (vol. 1, p. 401) gives them what I regard as the 

 c6rrect designation, "Arcus vert, occip." Though the lateral 

 portions of the occipital vertebra are here considerably larger 

 than the arches of a cervical vertebra this extra size is probably 



