The iris is a ring of coloured membrane lying just behind the cornea and surrounding the pupil of the eye. It is actually composed of minute sphincter and dilatormuscles, which govern the size of the pupil. Eye colour is determined by pigment deposits (yellow-to reddish brown). Blue eyes result when the absence of such pigment allows the purplish-black rear surface of the
iris to show. Occasionally a white pigment is present, which causes the iris to appear gray. Newborn babies generally have blue eyes, since they do not have much pigment at birth. Research Iris
The nasalis muscle consists of two parts: the alar and the transverse. The alar is used when the nostrils are flared and runs along the side of the nose. The transverse runs diagonally and is used to wrinkle the nose. The nasalis is composed of three small muscles: the compressor nasi, the dilator naris posterior, and the depressor septi nasi. The compressor nasi is a small, thin muscle with a triangular shape. It runs along the bridge of the nose and depresses the cartilage and compresses the alae together. The depressor nasi is a short muscle that lies between the musclular structure and the mucousmembrane of the lip. It arises from the upper lip and extends to be inserted into the septum of the nose. It constricts the nares (nostrils) of the nose, the opposite action of the compressor nasi muscle. The dilatornares posterior is a small muscle that originates from the edge of the nasal notch and is inserted into the skin near the edge of the nostril. This muscle works with the dilator naris anterior, which is located in front of it,
to dilate the opening of the nares. All muscles of the nose are supplied by the facial nerve. Research Nasalis
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Dilator
