The full, uncommented, version of this file is in the demodata directory in file dep.tri.
All lines have the same format:
NODE1 NODE2 NODE3 - the three nodes forming a triangle.
1 2 204 !NODE1 NODE2 NODE3 - the three node numbers for triangle 1
1 204 126 !NODE1 NODE2 NODE3 - the three node numbers for triangle 2
2 3 204
3 4 203
3 203 204
...
466 468 472
468 469 471
468 471 472
469 470 471