title: Anatomy and histology of the frontalis muscle.
abstract: OBJECTIVE
  To determine the gross and histologic configurations of the medial and lateral frontalis muscle.
  
  
  METHODS
  After making a midcoronal incision and bluntly dissecting to the orbital rim, the frontalis muscle was marked and measured. A protractor was used to measure the frontalis-orbicularis angle (FOA) and, when present, the angle of central bifurcation (AOB). Three strips of full-thickness forehead soft tissue measuring 0.5 cm × 8 cm were excised 3, 4.5, and 6 cm above the supraorbital notch and analyzed histologically for the presence of skeletal muscle fibers. Data were analyzed using 2-sample t tests, paired t tests, Pearson correlations, and mixed effect models. A p value of ≤ 0.05 was considered statistically significant.
  
  
  RESULTS
  Sixty-four hemifaces of 32 cadavers (16 males) were dissected. All specimens were Caucasian. The average age was 78.2 years (range, 56-102 years). The average FOA was 88.7° (13.0°), and the average AOB was 90.0° (26.4°). A visible midline bifurcation occurred in 28 of 32 subjects (88%) at an average height of 4.7 cm (range, 2.4-7.2 cm) superior to the supraorbital notch. Continuous skeletal muscle fibers were present within the midline bifurcation histologically in 89%, 75%, and 11% of specimens 3.5, 5.0, and 6.5 cm above the supraorbital notch, respectively. In 46% of individuals, skeletal muscle fibers were continuously present microscopically within the gross bifurcation.
  
  
  CONCLUSIONS
  While a medial frontalis muscle bifurcation occurs grossly in most senescent Caucasians, muscle fibers exist microscopically within this zone in nearly half of individuals.
authors.affiliation: *Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio; †Department of Anatomic Pathology, Cleveland Clinic, Cleveland, Ohio, U.S.A.; ‡Department of Ophthalmology, Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand; and §Department of Anatomy, Cleveland Clinic Lerner College of Medicine, Cleveland, Ohio, U.S.A.
authors.forename: Bryan R
authors.initials: BR
authors.lastname: Costin
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Plesec
authors.forename: Natta
authors.initials: N
authors.lastname: Sakolsatayadorn
authors.forename: Tal J
authors.initials: TJ
authors.lastname: Rubinstein
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: McBride
authors.forename: Julian D
authors.initials: JD
authors.lastname: Perry
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005138:Eyebrows / Q000033:anatomy & histology; D005152:Facial Muscles / Q000033:anatomy & histology* / Q000166:cytology; D005260:Female; D005546:Forehead / Q000033:anatomy & histology / Q000601:surgery; D005624:Frontal Bone; D006801:Humans; D008297:Male; D008875:Middle Aged; D009915:Orbit / Q000033:anatomy & histology / Q000601:surgery