Lumbar vertebral pattern variation in the common opossum (Didelphis marsupialis Linnaeus, 1758): implication on lumbar nerve distribution

The lumbar nerve distribution can differ depending on vertebral count variations among individuals of the same species. The variation in the lumbar vertebra formula and the lumbar nerve distribution in twenty adult common opossums (eight female and twelve males) was studied. Radiographs were taken to confirm vertebral identification and count. Two vertebral patterns were recognized: three specimens presented five lumbar vertebrae (5VP) and seventeen individuals presented six lumbar vertebrae (6VP). All the 6VP specimens had the same innervation pattern; however, the 5PV had three different innervation patterns (5PVa, 5VPB, and 5PVc). 5VPa and 6VP differed only in the origin of the lateral femoral cutaneous nerve (L2-L3 and L3, respectively). The differences among 5PVa, 5PVb, and 5VPc were seen in the iliohypogastric nerve, which was formed by L1 in 5VPa and 5VPb, and T13 in 5VPc. The ilioinguinal nerve was formed by L1-L2 in 5VPa and 5VPb, while it was formed by T13-L1 in 5VPc. The genitofemoral nerve was formed by L2-L3 in 5VPa, L2 in 5VPb, and L1-L2 in 5VPc. The cutaneous femoris lateralis was formed by L2-L3 in 5VPa and 5VPc, while it is formed only by L2 in 5VPb. The femoral and obturator nerves were formed by L3-L4 in 5VPa, and L2-L3 in 5VPb and 5VPc. The lumbosacral trunk originated from L4-L5-S1 in 5VP and L5-L6-S1 in 6VP. The data provided in this study may help understand the relationship between the spine and lumbosacral plexus variations and may find application in veterinary spine surgery.