The external anal sphincter consists of skeletal muscle. It is a complex sphincter and is described in various ways by different authors. There is the classical description and the newer two and one part descriptions.
The classical descritption is that there is the puborectalis and the external sphincter. The external sphincter consists of deep, superficial and subcutaneous parts.
A newer description of the external sphincter is that it conists of two parts; the deep and the superficial. The deep external sphincter in this model would correspond to a fusion of the puborectalis and deep parts in the classical description. The superfical external sphincter in this model would correspond to a fusion of the superficial and subcutaneous sphincters of the classical model. This model has some clinical relevance because it tallies with the appearances on magnetic resonance imaging.
A further alternative description is that there is just one sphincter complex which conists of the puborectalis and the three parts described in the classical description.
The main difference in the external sphincter between the sexes is that the external sphincter is much shorter anteriorly than posteriorly. In males the sphincter is more cylindrical.