is a double assertion, whose first part may be true, if we take Erectness strictly, and so as _Galen_ hath defined it; for they only, saith he, have an Erect figure, whose spine and thigh-bone are carried in right lines; and so indeed of any we yet know, _Man_ only is Erect. For the thighs of other animals do stand at Angles with their spine, and have rectangular positions in Birds, and perfect Quadrupeds. Nor doth the Frog, though stretched out, or swimming, attain the rectitude of _Man_, or carry its thigh without all angularity. [SN: _What seiante or sitting._] And thus is it also true, that Man only sitteth, if we define sitting to be a firmation of the body upon the _Ischias_: wherein if the position be just and natural, the Thigh-bone lieth at right angles to the Spine, and the Leg-bone or Tibia to the Thigh. For others when they seem to sit, as _Dogs_, _Cats_, or _Lions_, do make unto their Spine acute angles with their Thigh, and acute to the Thigh with their Shank. Thus is it likewise true, what _Aristotle_ alledgeth in that Problem; why _Man_ alone suffereth pollutions in the Night [SN: ἐξονειρωκτικός.], because _Man_ only lyeth upon his Back; if we define not the same by every supine position, but when the Spine is in rectitude with the Thigh, and both with the arms lie parallel to the _Horizon_: so that a line through their Navel will pass through the Zenith and Centre of the Earth. And so cannot other Animals lie upon their Backs: for though the Spine lie parallel with the _Horizon_, yet will their Legs incline, and lie at angles unto it. And upon these three divers positions in _Man_, wherein the Spine can only be at right lines with the Thigh, arise those remarkable postures, prone, supine and erect; which are but differenced in situation, or in angular postures upon the Back, the Belly and the Feet.