THE BALL OF THE EYE. 413 



1. The nasal, which arises from the parts about the internal 

 canthus of the eye. 



2. The anterior ethmoidal, which comes from the nose and 

 frontal sinus. 



3. Branches from the recti and obliqui muscles. ; 



4. The lachrymal vein, from the lachrymal gland and leva- 

 tor palpebrse muscle. 



5. Posterior ethmoidal vein, from the nose. 



6. The ciliary veins, or those of the choroid coat, which are 

 very numerous. 



7. The central vein of the retina, which is collected from 

 three or four principal branches, and follows the course of the 

 artery of the same name, through the cribriform part of the 

 sclerotic coat, and through the centre of the optic nerve. The 

 trunks of this vein anastomose, at the anterior margin of the 

 retina, with those of the Ciliary Body. 



There are, of course, frequent anastomoses between the- 

 veins of the eyelids and the primitive branches of the ophthal- 

 mic vein. 



SECT. II. OP THE BALL OF THE EYE. 



The Eyeball (Bulbus Oculi) is situated within the anterior 

 half of the orbit, from which it is kept separated by its auxili- 

 ary parts, and by a large quantity of adipose matter which fills 

 up their interstices. It is very nearly spherical, but not so 

 much so as to prevent its a ntero- posterior diameter, which is 

 about an inch long, from exceeding in measurement every 

 other. Such, at least, is the general opinion of anatomists* 

 but from experiments, made by distending the eye with mer-, 

 cury, I have been induced to doubt its correctness, and espe- 

 cially in the African; for, in the latter, I have uniformly found 

 the transverse diameter to exceed the antero-posterior by a line 

 or more. The Eyeball is also somewhat flattened at the inser- 

 tion of each of the straight muscles. 



It is formed by a series of concentric tunics* one investing 

 the other, and by humours contained within those tunics. Of 

 the former, the Selerotica and the Cornea are external, the Cho- 

 roidea and the Iris next, and the Retina is iaternaj. Of th^ 



36* 



