Sentence:  Captain went out in the cab all the morning. Harry came in after school to feed me and give me water. In the afternoon I was put into the cab. Jerry took as much pains to see if the collar and bridle fitted comfortably as if he had been John Manly over again. When the <WSD>crupper</WSD> was let out a hole or two it all fitted well. There was no check-rein, no curb, nothing but a plain ring snaffle. What a blessing that was! 
Meaning of the word marked with <WSD> tags:  A strap, looped under a horse's tail, used to stop a saddle from slipping.