Peripheral nerve anomalies and associated musculoskeletal defects in anuran species: New anatomical records

In this study, we analyzed peripheral nerve anomalies in 15 anuran species spanning multiple developmental stages. Anatomical examinations focused on both the central nervous system-including the olfactory bulbs, telencephalon, diencephalon, midbrain, cerebellum, and hindbrain-and the peripheral nervous system, with particular attention to cranial and spinal nerves. Spinal nerve anomalies were often associated with vertebral deformities such as scoliosis and commonly presented as nerve thinning, fusion, or asymmetrical branching along the curvature's concave side. Limb rotation primarily affected the elbow and extended to the hand, accompanied by variations in interstitial nerve branching. Specimens with cranial torsion exhibited smaller cerebral hemispheres, anterior displacement of the cerebellum, and atrophied or indistinct cranial nerves contralateral to the curvature. In the hindlimbs, phalangeal reductions in cases of brachydactyly correlated with absent or altered plantar interstitial nerves. Hemimelia was marked by the absence of distal nerves and severe underdevelopment of carpal and digital elements, while oligodactyly showed altered nerve orientation and reduced distal innervation. Some of these patterns parallel congenital nerve disorders in humans, offering insight into the evolutionary and developmental foundations of nerve malformations. Our findings contribute to a deeper understanding of vertebrate congenital anomalies and highlight the importance of future studies on their genetic, morphogenetic, and environmental underpinnings.