Taizong was overjoyed, and at once commanded his attendants: “Put the saddle on my own carriage-horse, and beg my royal brother to mount and ride back to court with me.”

朕御車馬 — the emperor's own carriage-horse. Not a horse from the stables: the animal that pulls the imperial conveyance, given to a monk to ride. 扣背, to fasten it on the back — buckle the saddle. The emperor is specifying the tack himself, which is what people do when they are excited and have nothing useful to hold. And 請, beg him to mount. The order is given to the attendants; the verb aimed at the monk is a courtesy.

The Tang monk gave thanks for the favour and mounted.

謝了恩 is the fixed formula for accepting an imperial gift, and it is all the reaction the novel gives him. Seven characters to get a buddha onto an emperor's horse. He has spent the whole journey on the white dragon-horse. He is now riding something else, and the animal that carried him a hundred and eight thousand lǐ is being led behind.

The Great Sage swung his gold-banded staff and followed close; Pigsy and Sha Monk steadied the horse and shouldered the load between them, and they went in behind the imperial train together into Chang'an.

Look at the formation. Monkey walks armed beside his master; Pigsy and Sha Monk take the horse and the luggage. It is the marching order they came down in at the end of the last passage, and nobody has told them to keep it. 扶馬 is to steady the horse rather than lead it — the dragon-horse is loaded, and two of them are minding it. 隨駕後 — behind the imperial carriage. The pilgrims enter their own capital at the back of a procession, on foot, carrying things. And 長安, the Lasting Peace, is read Cháng'ān: its first character is the one for length, not the zhǎng of an elder.