Not only did Herath reach the 400-wicket milestone and complete a century of Test wickets against Pakistan with his 6 for 43, he also became just the fourth bowler to take 100 fourth-innings wickets in Test history, joining Shane Warne (138), Muttiah Muralitharan (106) and Glenn McGrath (103). (To compare, 22 bowlers have achieved this feat in the first innings, 25 in the second, and 17 in the third.
Herath is the only bowler to take 100 fourth-innings wickets without completing the century in each of the other three innings: he has only 85 in the first and 92 in the third.
Given that the pitch is usually at its toughest in the fourth innings, bowlers should usually find it easier to be at their best, unlike batsmen, who often struggle for runs in the last innings of a Test. However, because matches often don't last that long, bowlers don't always get the opportunity to bowl in fourth-innings situations. In all of Test history, only 12.5% of all wickets taken by bowlers have been in the fourth innings; in each of the first two innings, the corresponding percentage is nearly 31. In the last ten years, when the frequency of outright results has increased, the percentage of fourth-innings wickets has gone up, but it is still only 15.4.
Seen in that context, Herath's numbers are quite remarkable. He has taken 100 fourth-innings wickets out of a career tally of 400, which works out to a round figure of 25%. His fourth-innings average of 18.38 is almost half his first-innings mean of 35.58.
Among the 30 bowlers with at least 300 Test wickets, only one bowler has a higher percentage of fourth-innings wickets: Mitchell Johnson took 80 of his 313 career wickets in the last innings, which is a percentage of 25.56. But Johnson also bowled a lot more in the fourth innings: 24.65% of his total deliveries were bowled then, which is almost a quarter of his total workload. Also, his fourth-innings average of 25.26 isn't that much better than his career average of 28.40.
In Herath's case, though, the difference is much starker. Just 19% of his career deliveries have fetched him 25% of his career wickets in the fourth innings. Also, his average of 18.38 in the last innings is much better than his overall career average of 27.82.
Whichever way you slice the fourth-innings data, Herath emerges at the top. In terms of the ratio of career to last-innings average, Herath's 1.51 is better than anyone else's. He also has 11 five-fors in that innings, four more than Murali and Warne.
Among the other bowlers who have much better stats in the last innings compared to their career numbers are Chaminda Vaas and Anil Kumble. Vaas averaged 20.43 in the fourth innings, and took around 16% of his career wickets in that innings, while Kumble averaged 22.39, compared to his career average of nearly 30. Richard Hadlee has excellent numbers too, though he hardly got opportunities to bowl in the last innings. In a career spanning 86 Tests and almost 22,000 deliveries, he bowled in the fourth innings only 20 times, sending down a grand total of 1261 balls. The balls bowled percentage of 5.75 is the lowest among all bowlers in the 300-wicket club.
At the other end of the spectrum are bowlers for whom the fourth innings contributed minimally to their career numbers. Hadlee belongs there as well due to limited opportunities, while the other great allrounders of the era didn't do much either. Imran Khan averaged a shocking 42.09 in the fourth innings, almost twice his career average, while Ian Botham conceded more than 38 runs per wicket. For Zaheer Khan and Kapil Dev too, the contribution of fourth-innings wickets was less than 9% of the career wickets, while in terms of poorest ratio of averages, Imran and Botham occupy the top two spots.