Pilonidal sinus of the penis

A pilonidal sinus is a subcutaneous sinus containing hair. It is most commonly found in the natal cleft of hirsute men. Here we describe the unusual finding of a pilonidal sinus arising on the male foreskin.     

Functional morphology of the human chin

The protruding chin is an attribute that defines modern Homo sapiens to the exclusion of all other primates, including fossil hominids. The functional significance of the chin has been contemplated for most of the 20th century, but as yet no compelling functional argument for its evolution has withstood careful scrutiny. Consequently, the human chin is often cited as an example of a nonadaptive trait. Past attempts to explain the chin in a functional or mechanical context have failed, largely as a result of an incomplete understanding of in vivo masticatory biomechanics. When the morphology of the chin is considered in light of experimental data on mastication, its evolution can be interpreted as a consequence of recent changes in mandibular proportions that have altered the relative importance of different masticatory stresses. Hypotheses proposing that chin morphology is the result of sexual selection or spatial constraints may be untestable. As with arguments that posit no functional role for the chin, the credibility of these hypotheses has depended, to a large degree, on the refutation of previous biomechanical explanations.     

Surgical correction of the vertically deficient chin

Surgical correction of the vertically deficient chin has received relatively little attention. This paucity of information is most likely related to the failure to diagnose vertical microgenia and the questionable stability of its surgical correction utilizing autogenous bone grafts. This paper reports on eight patients who have undergone vertical augmentation genioplasty utilizing a transverse symphyseal osteotomy and interpositional implantation of porous, block hydroxyapatite. All patients had preoperative measured decreases in lower face height. Mean vertical lengthening of the chin was 5.3 mm. Seven of the eight patients had class II occlusions and underwent simultaneous sagittal advancement of the chin. Follow-up at a mean time of 11.1 months revealed complete stability of the vertically repositioned symphyseal segment. Mean ratio of the vertical soft to hard tissue augmentation was 0.89:1. There were no instances of operative complications. Vertical facial aesthetics and their application in the evaluation and treatment of patients with vertically deficient lower faces and chins are reviewed.     

The enduring puzzle of the human chin

Although modern humans are considered to be morphologically distinct from other living primates because of our large brains, dexterous hands, and bipedal gait, all of these features are found among extinct hominins. The chin, however, appears to be a uniquely modern human trait. Probably because of the chin's exclusivity, many evolutionary scenarios have been proposed to explain its origins. To date, researchers have developed adaptive hypotheses relating chins to speech, mastication, and sexual selection; still others see it as a structural artifact tangentially related to complex processes involving evolutionary retraction of the midfacial skeleton. Consensus has remained elusive, partly because hypotheses purporting to explain how this feature developed uniquely in modern humans are all fraught with theoretical and/or empirical shortcomings. Here we review a century's worth of chin hypotheses and discuss future research avenues that may provide greater insight into this human peculiarity.