266 Vertebrate Embryology 



column were formed, forms also a part of the 

 cranium. It extends in the middle line along 

 the under (ventral) side of the brain as far 

 forward as the hinder edge of the pituitary 

 body. On each side of this anterior part 

 of the notochord is developed a horizontal 



all 



FIG. 80. EGG OF CHICK WITH EMBRYO AND 

 FCETAL APPENDAGES. (After Parker and Haswell, 

 from Duval.) 



a, air-space, a//, allantois. am, amnion. ar. vase, area 

 vasculosa. emb^ embryo, yk^ yolk-sac. 



sheet of cartilage. These two sheets of car- 

 tilage, the parachordal plates, lie in close con- 

 tact with the notochord, and, with it, form a 

 broad floor for the hind- and mid-brains. The 

 two parachordal plates fuse together, above 

 and below the notochord, thus enclosing the 

 latter, to form the so-called basilar plate which 

 forms the floor of the hinder part of the skull. 

 To the sides of the basilar plate are fused the 



