Balin took the contract from Bilbo, fishing the magnifier out of his pack and examining the signature closely to make sure it was genuine. After looking it over, the dwarf gave a satisfied nod. 
"Everything seems to be in order." he agreed. "Welcome then, Bilbo Baggins, to Thorin Oakenshield's company."
"Get him a pony." Thorin ordered sharply, urging his own mount onward. They had wasted enough time already, they needed to make up for it by getting back on the road quickly.

The spare pony was brought up from the back of the group and the reigns were handed to the hobbit, before the other dwarves all headed after Thorin, expecting that Bilbo already knew how to ride, so they didn't wait for him.