Something I have been saying for years, my boy carries lines through all of the listed stallions except for Orange Peel (Fr) one US stallion and a Pharos full brother but there are plenty of Pharos crosses in his pedigree.
As for flexibility of the spine The Tetrach had incredible mobility in so far as his hind legs could stretch well beyond his forelegs in the gallop which made him a bit gormless when not travelling at speed, an accident waiting to happen he cut into himself and ruined any future he may have had on the track as he was as good a distance horse as he was a sprinter. Equally sadly he was proved sterile early in his life although he lived until he was about 30. Here endeth the lesson.