Charles Sedgwick Minot 



95 



factory interpretation seem to me lacking. In amphibia (as in nec- 

 turus) there is at first a well-defined velum ; the mesenchyma within the 

 velum increases greatly in amount and converts the velum into a broad 

 structure, Fig. 13, V. I have been unable as yet to follow the growth 

 of the velum in sufficient detail, but it is probable that, as the velum 

 expands, the post-velar arch is incorporated in it and disappears as a 

 separate region. The enlarged velum projects backward, extending 



Fiq. H 



Fig. 14. Chick embryo of about 7.0 days. Sagittal series, 3.54, section :204. x 30 

 diams. 



even into the mid-brain, and meanwhile expands laterally around and 

 in front of the paraphysal arch, until its wings meet across the median 

 line, Fig. 13, pi. x, to form the anlage of the anterior plexus. The 

 entire expanded velum gives rise to the choroid plexus (supra-plexus of 

 American writers), which accordingly surrounds the paraphysis. In 

 the adult the paraphysis has become a gland of complex structure, as 

 has been so well described by Francotte, but by most writers has been 

 conftised with choroid plexus. In Bana haleciiia I find the adult 



