162 ANTHROPOLOGY. 



orbits, eyebrows, eyelids, conjunctiva, lachrymal apparatus, muscles of the 

 eye, and ocular fascia, with their several blood-vessels and nerves. # 



The Orbits. These are conical bony recesses, the sides of unequal 

 length, and joined to each other at angles so as to form quadrangular pyra- 

 mids : seven bones enter into their formation, the frontal, sphenoid, ethmoid, 

 malar, maxillary, unguis, and palate. The axis or central line of the orbits 

 leads obliquely from the apex forwards and upwards and a little downwards. 

 If, therefore, the axes of both orbits be produced, they will diverge con- 

 siderably in front, but meet rapidly behind, intersecting at the back of the 

 body of the sphenoid bone. These lines are not parallel to the axes of the 

 eyeballs, which lead more directly forwards and are nearly horizontal. 

 -The foramina in the orbit are : 1. The optic^ which transmits the optic 

 nerve, and beneath this the ophthalmic artery. 2. The foramen lacerum 

 superius or sphenoidal fissure, the larger inner end of which corresponds to 

 the axis of the orbit, and transmits the third, fourth, ophthalmic division of 

 the fifth, and the sixth cerebral, and filaments of the sympathetic nerves. 

 Beneath these the ophthalmic vein escapes from the orbit to join the cavern- 

 ous sinus. The external part of this foramen is closed by membrane, 

 through which a small artery from the middle meningeal sometimes passes 

 and assists in supplying the lachrymal gland. 3. The lacerum inferius or 

 gpheno-maocillary fissure is in the inferior external angle of the orbit, and 

 transmits small nerves and vessels from the orbit to the zygomatic fossa. 

 4. Internal orbital foramina, generally two, but sometimes more, are in the 

 superior internal angle ; the anterior transmits the nasal twig of the ophthal- 

 mic nerve ; the posterior, the ethmoidal branch of the ophthalmic artery. 



1. The Supercilia, or eyebrows, bound the superior eyelids ; they 

 correspond to the superciliary ridge of the frontal bone, which partly causes 

 their prominence. The hairs of the eyebrows are mostly directed in a 

 slanting manner outwards, and are placed in two rows, the superior directed 

 downwards and outwards, the inferior upwards and outwards ; both rows 

 converge in a median ridge, which causes a greater fulness and an even, 

 regular appearance. The e3-ebrows are of use in shading the eye from 

 very strong light, and protecting it from particles of dust and from perspira- 

 tion and other fluids. They can be moved in three directions : upwards, 

 by the occipito-frontalis muscle ; downwards, by the orbicularis ; down- 



. wards and inwards, by the corrugators. 



2. Palpebr^, or Eyelids. These are the two movable semilunar 

 curtains, or folds of skin, placed in front of each orbit, convex and rounded, 

 with horizontal wrinkles, and exactly moulded to the eye. The opening 

 between them is called the palpebral fissure or rima. When the lids are 

 open, they circumscribe an aperture more or less elliptical, on the size of 

 \yhich the apparent magnitude of the eye greatly depends. Its extremities 

 are called canthi. The outer canthus is an acute angular commissure 



. a little rounded, about a quarter of an inch distant from the edge of the 



orbit, to which it is attached by a dense fibrous membrane. The innei 



canthvs extends for a short distance inwards towards the side of the nose, 



the edges being a little rounded ; externally it presents a small tubercle on 



868 



