A Novel Organizational Pattern of the Nasofrontal Complex in Plecotus auritus Revealed by Micro-Computed Tomography.

The nasofrontal region of mammals is generally characterized by direct contact between the paired nasal bones and the frontal bone. However, detailed spatial relationships among the frontal bone, nasal bones, and osseous nasal septum remain insufficiently documented in bats. This study investigated the three-dimensional organization of the nasofrontal complex in the brown long-eared bat (Plecotus auritus) using high-resolution micro-computed tomography. Ten adult skulls were analyzed using three-dimensional reconstructions and multiplanar image analysis. A consistent and previously undescribed organizational pattern was identified in all specimens. Its principal feature was a median rostral extension of the frontal bone, designated processus internasalis ossis frontalis (nova structura), which projected between and separated the caudal portions of the paired nasal bones. This structure was consistently associated with ala ossis nasalis (nova structura), facies parasagittalis ossis nasalis (nova structura), a pronounced internasal sagittal impression, and a close topographical relationship with the osseous nasal septum. Together, these features constitute an integrated morphological complex rather than isolated anatomical modifications. The observed arrangement differs from the generalized mammalian condition, in which the paired nasal bones maintain direct median contact at the nasofrontal boundary. These findings reveal a distinct pattern of nasofrontal organization in P. auritus and demonstrate the value of high-resolution micro-computed tomography for identifying previously unrecognized aspects of mammalian cranial anatomy.