What is the ' neck' of rugae? Can you please give a diagram of neck?

Dear student, 
​Please find below the solution to the asked query        

Rugae is a term that commonly means series of ridges produced by folding of the wall of an organ. 

The innermost layer  forms irregular folds  in the stomach called rugae. Gastric rugae can also be called  gastric folds. They allow the stomach, or other tissue, to expand when needed, as in time when  the stomach fills. The rugae in stomach unfolds at the time of filling in order to provide more surface for food. Other than stomach, they are found in vagina, urinary bladder, scrotum and gall bladder.

There is no neck in rugae as these are in foldings in an organ.

Hope this information will clear your doubts about the topic.    Regards