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turned upwards: tlie septum orbitale, and the oilier turned down 

 the septum nasale. 



Fig. 3. Fig. 4. 



Now, two things should be observed : First that the prechordal plate 

 extending in front of the Hj'pophysis, forms an angle with the basicranial 

 plate behind it. This angle which is still more distinct in younger 

 embrjos, is identical with the sphenoida angle, the tj'pical feature of the 

 orthognathous human skull. The second thing to be observed is the 

 direction of the septum nasale. In this young Lacerta embryo the 

 axis of this septum is perpendicular to the base of the skull, which 

 also is a typical feature of the orthognathous human skull. In pas- 

 sing, I wish to point out that in this phase of development the 

 entrance to the mouth is, in Lacerta, not apical, but points down- 

 ward. This reminds us incontinently of the permanent condition in 

 Plagiostomes. 



So the verticality of the septum nasale is a characteristic which, in 

 this phase of development, the head of the Lacerta-embryo has in 

 common with the orthognathous type. Fig. 4 shows how this type 

 passes into the prognathous. In fig. 4« the median section through 

 a primordial cranium is given, head length 4.5 mm. In fig. 4* 

 the same with a length of 5 mm.; the enlargement in the two 

 figures differs. Relative to the younger stage, the septum orbitale 

 in the embryo with a head length of 4.5 mm. is considerably enlarged. 

 It is clear that the axis of the nasal septum is no longer perpen- 

 dicular to the base of the skull, but has rotated anteriorly. In the 

 5 mm. embryo this rotation is so considerable that the axis of the 

 Septum nasale is nearly on a level with the base of the skull. In 

 this older embryo the septum orbitale exhibits marked signs of 



