Whose ribs? Ichabod's?

" Another convulsive kick in the ribs" = " Another convulsive kick made by the black steed in Ichabod's ribs?"

Context:

An opening, in the trees now cheered him with the hopes that the church bridge was at hand. The wavering reflection of a silver star in the bosom of the brook told him that he was not mistaken. He saw the walls of the church dimly glaring under the trees beyond. He recollected the place where Brom Bones' ghostly competitor had disappeard. "If I can but reach that bridge," thought Ichabod, " I am safe." Just then he heard the black steed panting and blowing close behind him; he even fancied that he felt his hot breath. Another convulsive kick in the ribs, and old Gunpowder sprang upon the bridge; he thundered over the resounding planks; he gained the opposite side; and now Ichabod cast a look behind to see if his pursuer should vanish, according to rule, in a flash of fire and brimstone. Just then he saw the goblin rising in his stirrups, and in the very act of hurling his head at him. Ichabod endeavored to dodge the horrible missile, but too late. It encountered his cranium with a tremendous crash, --he was tumbled headlong into the dust, and Gunpowder, the black steed, and the goblin rider, passed by like a whirlwind.

More:

http://www.virtual-arts.com/stories/sleepyhollow/page06.html