頸袋 is read as けいたい (keitai) and means dewlap.
けいたい
keitai
てぶくろ
glove
ふくろ
dead end
かみぶくろ
paper bag
おふくろ
one's mother
たび
tabi
いぶくろ
dietary needs
じかたび
work tabi
ちえぶくろ
all one's wisdom
ねぶくろ
sleeping bag
かんにんぶくろ
one's store of patience
せちべんたび
something worn over tabi to keep them from getting dirty
てさげぶくろ
handbag