鋸下四隻角 Four Horns Sawn Off
少頃間，八戒發起性來，掣出戒刀，將辟塵兒頭一刀砍下，又一刀把辟暑兒頭也砍下。隨即取鋸子鋸下四隻角來。孫大聖更有主張：就教四位星官將此四隻犀角拿上界去，進貢玉帝，回繳聖旨。把自己帶來的二隻，留一隻在府堂鎮庫，以作向後免徵燈油之證；自己帶一隻去，獻靈山佛祖。四星心中大喜。即時拜別大聖，忽駕彩雲回奏而去。少顷间，八戒发起性来，掣出戒刀，将辟尘儿头一刀砍下，又一刀把辟暑儿头也砍下。随即取锯子锯下四只角来。孙大圣更有主张：就教四位星官将此四只犀角拿上界去，进贡玉帝，回缴圣旨。把自己带来的二只，留一只在府堂镇库，以作向后免征灯油之证；自己带一只去，献灵山佛祖。四星心中大喜。即时拜别大圣，忽驾彩云回奏而去。
逐句解 Line by line
In a little while Eight Rules worked himself into a temper, drew out his precept-knife, and with one stroke cut off Dust-Averting's head, and with another stroke cut off Heat-Averting's head as well.
The sentence is carried out and it is Eight Rules who carries it out — without being told, in a temper, with a knife that is not a weapon. A 戒刀 is a precept-knife, the small blade a monk carries under the monastic rule for cutting cloth and shaving. Using it for a beheading is a detail the novel offers without comment.
Then they took a saw and sawed off the four horns.
Eleven characters, and the chapter's second title-line is complete. Two creatures, two horns apiece, four horns.
The Great Sage Sun had a further proposal: he had the four star officers take these four rhinoceros horns up to the world above as tribute to the Jade Emperor, and to return the sagely decree at the same time.
更有主張 has 更 as gèng, meaning "further" — not the night-watch sense it took at the start of the chapter. 回繳聖旨 is to hand back the decree, that is, to close the file. The horns are being used as the receipt.
Of the two he had brought himself he left one in the prefectural hall to hold the treasury, as evidence for the remission of the lamp-oil levy hereafter;
This is the shrewdest thing anybody does in the chapter. 鎮庫 is to hold down or steady a treasury — a valuable kept as a talisman against loss. But the stated purpose is legal: 以作向後免徵燈油之證, as evidence for the future remission of the lamp-oil levy. Pilgrim is leaving a physical exhibit in a government office so that no future prefect can restart the tax.
and one he took with him, to present to the Buddha Patriarch on Spirit Mountain.
靈山 is Spirit Mountain, the Buddha's own seat and the pilgrims' destination — still eight chapters away. The horn is going the whole remaining distance as a gift.
The four stars were greatly pleased in their hearts.
Six characters. They are pleased because they now have tribute to carry, which turns a routine assignment into a creditable one.
They took their leave of the Great Sage on the spot, and on a coloured cloud went off to make their report.
回奏 — to go back and report to the throne. The four constellations leave the chapter as they entered it: on official business, with paperwork to complete.
Four horns, four destinations, and every one of them thought through. Four go up to the Jade Emperor as tribute, which doubles as the four stars' proof that the decree was executed. One stays in the prefectural treasury as legal evidence. One travels the remaining eight chapters to Spirit Mountain as a gift to the Buddha.
The one left in the treasury is the cleverest. Pilgrim's stated reason is that it will serve as evidence for the future remission of the lamp-oil levy — a physical object in a government office, so that when everyone who saw the coloured cloud is dead, the next prefect who fancies reviving a fifty-thousand tael annual offering will have a rhinoceros horn in the strongroom telling him why not. It is a monkey thinking about institutional memory.
And Eight Rules carries out the execution himself, in a temper, with the small knife a monk keeps for cutting cloth. The novel spends one line on it. Two creatures whom a whole town worshipped as Buddhas for years lose their heads on a prefectural floor to the least dignified member of the party, and the text moves straight on to the disposal of assets.