Nub/skull theory??

[baileybubs]

Hi ladies, my question is relating to gender guesses, what is skull and nub theory? I have read people mention it but dont know what it is exactly!

And based on these scan photos any gender guesses?

https://i1150.photobucket.com/albums/o619/baileybubs/9FA8ED2B-CC20-41B9-9501-BC74093E9FE3-8469-00000A0B0C217DD0_zps01d49c45.jpg

https://i1150.photobucket.com/albums/o619/baileybubs/E615FBD9-2F50-45FE-8C07-54A43705510F-8469-00000A0B062B1B7D_zps785e8392.jpg

If the pictures are clear enough to see!

 

[baileybubs]

Bump

 

[baileybubs]

Bump