36o 



ORR. 



[Vol. I. 



other in the median line, the primary inner (shaded) surface 

 becomes the external surface, while the anterior curve («) bends 

 as seen at C. The relations of the surfaces in the region of the 

 curve, in C, are not the same as found in the embryo, for the 

 primary outer surface still faces outward. If, however, the up- 

 per edge of the anterior curve be held inward at the same time 

 that the two ends are brought flat together, a form is produced 

 similar to that represented at D. Making allowances for the 



DIAGRAM II. 



difference in texture and in the surrounding media, the form D 

 permits a comparison with Goette's description of the neural 

 growths in Bombinator. At k is seen the " Knickungsstelle " 

 and " hervortretende Hirnplatte," and at a is the " Tasche " to 

 which he refers. Could the primitive lateral and anterior bands 

 of nerve-fibres which I have described in the nervous system of 

 the lizard be removed entire, their form would correspond 

 almost exactly with the form D. The supposition that the 

 cranial flexure may have been partly caused in the manner just 

 described, agrees with the fact that in the amphibian and lizard 

 embryos the primary cranial flexure forms during the period of 

 the closing in of the medullary groove. I judge, from Balfour's 

 description, that this is also the case in the elasmobranch embryo. 

 In other accounts relating to this subject, the attention not hav- 

 ing been directed to this point, the descriptions of it are too 

 obscure to admit of certainty. I have previously referred to 

 mechanical influences in the secondary cranial flexure. 



The connection of the notochord with the hypophysis in the 

 lizard is a point worthy of mention. The exact relations of the 

 anterior end of the notochord have rarely been traced out in all 

 the early stages of development, and it is possible that more ex- 



