Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
F1: The sciatic nerve issues from the pelvis and remains
divided into peroneal and tibial divisions passing beneath m.
piriformis which in this case has two bellies.
F2: The sciatic nerve issues from the pelvis divided into peroneal and tibial divisions. The peroneal division passes through the division of m. piriformis.
F3: Similar to preceding, m. piriformis is divided allowing passage of the peroneal division of the sciatic nerve.
F4: The sciatic nerve issues from the pelvis divided into peroneal and tibial divisions, which unite after passing through the divided m. piriformis. The superior part of piriformis is joined with m. gluteus minimus and the inferior part has two bellies. In this case the tibial division passes through the division and the peroneal division passes above m. piriformis.
F5: Similar to D, except the union of the division of the sciatic nerve takes place at a lower level.. at the tendon of m. obturator internus.
F6: Similar to D and E except that the larger superior division of m. piriformis is intimately united with m gluteus medius.
F7: The sciatic nerve issues from the pelvis as usual beneath piriformis, but m. piriformis is divided into a smaller superior part and a larger inferior part.
F8: The sciatic nerve issues from the pelvis divided, but rejoins immediately below m. piriformis which is completely divided into two parts.
a, M. gluteus medius; b, m. gluteus minimus, which has a part (c) separated by a deep sulcus (A, C, H); d, e, m. piriformis with two bellies: the upper belly is small (d) and the inferior belly (e) is large (A-C, G); d+, e+, m. piriformis duplicated: the upper muscle is larger (d+) and the lower muscle is smaller (e+): d2, e2, m. piriformis duplicated, united by a single tendon (D): d3, e3, m. piriformis duplicated and intimately united with
m. gluteus medius (E); d4, e4 , m. piriformis intimately united with m. gluteus medius which has a distinct, partial, division (c); f, g, mm. gemelli; h, m. obturator internus; i, m. quadratus femoris.
From Calori, L. Sull'alta divisione del nervo grande ischiatico considerata come differenza nazionale e sulle varieta del muscolo piriforme. Mem. R. Accad. Sci. Istituto di Bologna S. 4, 2:623-633. 1880.
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