FIRST HALF OF SECOND DAY 



473 



anterior neuropore 



osenccphalon 



metencephaJon 



myctencephalon 



E 



Fig. 278. 



Diagrams showing neuromeres in brain region of the neural tube. A, lateral 

 view of neuralplate of 24 hour chick embryo. B, dorsal view of brain from a 26- 

 27 hour (7 somite) chick embryo. C, dorsal view of brain from a 30 hour (10 

 somite) chick embryo. D, Dorsal view of brain from a 36 hour (14 somite) chick 

 embryo. E, Diagram of the segments (neuromeres, myotomes, etc.) of the head 

 in longitudinal section. A, anterior myotome ; a, abducens nerve ; b, branchial 

 clefts ; /, facial nerve ; g, glossopharyngeal nerve ; h, hypoglossal nerve ; I, lens 

 surrounded by layers of eye ; n, nasal pit with the terminal nerve nearby ; o, 

 oculumotor nerve ; op 5 , ophthalmicus profundus part of fifth nerve ; O8 5 ; ophthal- 

 micus superficialis part of the fifth nerve ; ot, otocyst ; a, spiracular cleft ; t, 

 trigeminal nerve ; to, truncus arteriosus ; tr, trochlearis nerve ; I- VIII, neuromeres ; 

 1-6 myotomes. (A-D, from Patten after Hill, E, from Kingsley after Neal.) 



