The ciliary body consists of both mesodermal (uveal) and ectodermal (retinal) portions. It runs round the eye as a slightly asymmetrical girdle, narrower on the nasal side and above (4-5 to 5-2 mm.) and broader on the temporal side and below (5-6 to 6-3 mm.). It is triangular in section, the apex being continous with the choroid, while the base is turned slightly towards the centre of the cornea. Its outer edge is attached to the scleral spur forming the anterior uveal insertion ring ; its inner edge is free and juts out just anterior to the equator of the lens. Its external surface abuts against the sclera, the perichoroidal space intervening. The internal surface faces the vitreous and is continous with the internal surface of the retina which ends in a scalloped margin, the ORA SERRATA.