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The [lumbar triangle] is a well-defined triangular space in the posterolateral lumbar region. Also known as the inferior lumbar triangle, its boundaries are: inferior, the iliac crest; anteromedial: latissimus dorsi muscle; posterolateral: posterior border of the external oblique muscle. The triangle has a superior apex, and the floor of the triangle is the internal oblique muscle.
The triangle is named after Jean-Louis Petit (1674 - 1750), a French Surgeon who is said to have been an anatomy teacher at an early age and became a surgeon when he was only eighteen!
The lumbar triangle is an area that is not as thick as the rest of the abdominal wall and as such it is a site of potential weakness that can lead to a lumbar hernia, also known as Petit’s hernia.
Sources:
1. “Jean Louis Petit – A Sketch of his Life, Character, and Writings” Hayne, AP San Fran Western Lancet 1875 4: 446-454
2. “Oeuvres compl?tes de Jean-Louis Petit” 1837 Imprimerie de F. Chapoulaud
3. Extraits de l'eloge de Jean-Louis Petit Ius dans Ia seance publique de I' Academie Royale de Chirurgie du 26 mai 1750” Louis A. Chirurgie 2001: 126 : 475- 81