THE ARGUMENT APPLIED. 3i 



tion in the bone as large as a goose-quill.* When once the 

 fluid has entered the nose, it spreads itself upon the inside o^ 

 the nostril, and is evaporated by the current of warm aii 

 which in the course of respiration is continually passing ovei 

 it. Can any pipe or outlet for carrying off the waste liquoi 

 from a dye-house or a distillery, be more mechanical than 

 tliis is ? It is easily perceived that the eye must want moist- 

 ure ; but could the want of the eye generate the gland which 

 produces the tear, or bore the hole by which it is discharg- 

 ed — a hole through a bone ? 



It is observable that this provision is not found in fish— 

 the element in which they live supplying a constant lotion 

 to the eye. 



It were, hoAvever, injustice to dismiss the eye as a piece 

 of mechanism, without noticing that most exquisite of all 

 contrivances, the nictitatiiig mcinbrane,\ which is found in 

 the eyes of birds and of many quadrupeds. Its use is to 

 sweep the eye, which it does in an instant — to spread over 

 it the lachrymal humor — to defend it also from sudden inju- 

 ries ; yet not totally, when drawn upon the pupil, to shut 

 out the light. The commodiousness with which it lies fold- 

 ed up in the inner corner of the eye, ready for use and ac- 

 tion, and the quickness with which it executes its purpose, 

 are properties known and obvious to every observer ; but 



* Plate I., Fig. 3. a, is the l(X(L'f^mal gland^ which supplies this 

 fluid ; it is situated at the outer and upper part of the orbit of the 

 eye, and secretes or separates tears from the blood. There are five or 

 six ducts or tubes, 6, which convey this fluid to the globe of the eye, 

 for the purpose of keeping it moist and facilitating its movements : 

 the motion of the eyelid difl"uses the tears, and c, c, the puncta lachry- 

 malia^ take up the superfluous moisture, which passes through rf, th<= 

 lachrirnal sac and duct, into the nostril at e. 



t Plate I., Fig. 4. The nictitating membrane, or third eyelid, is 

 a ^iiin, semitransparent fold of the conjunctive, which in a state of 

 rfest lies in the inner corner of the eye, with its loose edge nearly ver- 

 tical, but can be drawn out so as to cover the whole front of the eye- 

 ball. By means of this membrane, according to Cuvier, the eagle is 

 enabled to look at the sun. 



