790 



PHYSIOLOGY. 



space lying between it and the sclerotic. There are some unstriped 

 muscular fibers in the capsule of Tenon. These muscular fibers are 

 innervated by the cervical sympathetic, and project the eyeball when 

 in action. 



Intraocular Pressure. The intraocular pressure depends upon 

 the tension of blood in the arteries of the eye. The pressure under- 

 goes oscillations simultaneous with the pulse and respiratory move- 

 ments. 



The pressure is about 20 to 30 millimeters of mercury. 



Fig. 340. Schematic Eye three Times Natural Size. (LANDOLT.) 



0', Anterior or principal focus. A, Anterior surface of cornea. H' and R", 

 Principal points. K' and K", Nodal points. 0". Posterior or second principal 

 focus. F.c, Fovea centralis. 0', 0", Optic axis. 



The aqueous humor, which is secreted and absorbed with great 

 ease, appears to regulate the pressure. 



LYMPHATICS. The lymphatics of the eye comprise an anterior 

 and posterior set. The former is located in the anterior and posterior 

 chambers of the eye and has communication with the lymphatics of 

 the iris, ciliary processes, cornea, and conjunctiva. The posterior 

 set consists of the perichoroidal spaces lying between the choroicl 

 and sclerotic coats of the eyeball. 



