The risorius is a very thin muscle and is one of the superficial muscles of facial expression, which is reported as being inconstant, as it is absent in most people, and is a unique muscle; once it has no bony origin. The study aimed to report a different pattern of arrangement of the risorius muscle fibers. During a routine Anatomy class, a different pattern of arrangement of the risorius muscles fibers was found from the observation of an adult (around 40 years old) male cadaver hemiface (right side). After dissections, it was possible to note that the arrangement of the risorius muscle fibers on the surface of the masseteric fascia was formed in different arrangements formed in two bands. In conclusion, the risorius muscle fibers are not always easily distinguishable, and detailed knowledge of their different morphological arrangement is essential when planning and performing facial procedures.

The posterior wall of the orbit is composed by the sphenoid bone and exhibits the optic canal (OC) and the superior orbital fissure (SOF). The comprehensive knowledge of anatomical and morphometric observations of OC and SOF is vital for an accurate diagnosis and management of local pathology. The aim of this study was to conduct a morphometric analysis of the OC and the SOF in CT scans in a Brazilian population. A total of 40 computed tomography (CT) scans of dry human skulls were used (20 males and 20 females). The images were submitted to a segmentation in which the bony structures of interest in the orbit were selected. A three-dimensional reconstruction of the region and the measurements of the perimeter (mm) of the SOF and the volume (mm3) of the OC were performed. The statistical analysis was performed to verify if there was a difference in sex on each side for each anatomical structure. Regarding the OC, for the left side, there was a statistical difference between the sexes. For the SOF, neither the right side nor the left side showed statistical difference between the sexes. The present study showed new data about anatomical structures of the human orbit, bringing relevant knowledge for surgical and diagnostic procedures in the region. Especially for those anatomical structures evaluated that allow the passage of blood vessels and nerves, specific knowledge of their dimensions in different populations is valuable to avoid injuries during procedures in the orbital region.