by Aaron G. Filler, MD, PhD
Figure 10-2 – Additional Modification of Great Ape Lumbar Vertebrae.
A – Orangutan facet locks and gorilla laminar blocks – The orangutan and the gorilla have independently evolved different mechanical blocks that limit extension of the lumbar spine and prevent hyperextension in quadrupedal, diagonograde posture.
A1 – Lateral view of orangutan lumbar vertebra: the inferior facet is close to the pedicle (compare with human configuration in figure 9-2) and a locking extension assures hard bone to bone contact with the superior facet of the next lower vertebra.
A2 – Dorsal view of gorilla vertebra showing the groove on the superior facet and notch in the lamina that that limit extension.
B – Comparative superior view of gorilla, chimp and human vertebrae. Notice the thin flat lumbar transverse process in the chimpanzee.
A - From: Filler, A. G. (2007a). Homeotic evolution in the Mammalia: Diversification of therian axial seriation and the morphogenetic basis of human origins. (forthcoming).
B - From: Owen, R. (1857). Osteological contributions to the natural history of the chimpanzees (Troglodytes) and orangs (Pithecus). No. V. Comparison of the lower jaw and vertebral column of the Troglodytes gorilla, Troglodytes niger, Pithecus satyrus, and different varieties of the human race. Transactions of the Zoological Society of London, (printed 1862) 4(4): 89-115.