412 NERVOUS SYSTEM. 



end of the orbicularis, where it anastomoses with the palpebral 

 arteries. 



9. The Arteria Frontaiis passes out of the orbit near the su- 

 pra orbitary foramen. It is quickly divided into branches, which 

 go to the orbicularis and corrugator muscles, to the occipito- 

 frontalis, and to the frontal sinus. 



Of the Veimofthe Orbit. 



The blood distributed to the eye-ball and to its auxiliary parts, 

 has two routes for returning to the heart, one through the ca- 

 vernous sinus, and the other by the superficial veins of the face. 

 As a general rule, all the branches of the ophthalmic artery 

 which reach the eyelids, or become otherwise superficial, re- 

 turn their blood by the latter route; and those whose distribu- 

 tion is to the ball of the eye and to the parts deeply seated in 

 the orbit, return their blood by the sinus. 



When the veins are well injected, a very considerable num- 

 ber is manifested in both eyelids. They form a handsome net- 

 work, the meshes of which are small and numerous, and com- 

 mence by small roots at the margin of the eyelids. The ves- 

 sels of this net- work becoming, successively, larger from the 

 centre to the circumference of the orbicularis, cover the whole 

 surface of the latter, and from the thinness of the skin are 

 readily seen beneath it. The veins of the lower eyelid are 

 discharged into the facial vein, where it borders on the orbi- 

 cularis; and the veins of the upper lid, being bordered along 

 ihe superior margin of the rbicularis by a horizontal branch 

 of the temporal vein, discharge themselves into it. 



The Ophthalmic Vein (Sinus Ophthalmicus) is the large 

 trunk within the orbit which receives, successively, the re- 

 maining blood of the eye, and passing along the internal parts 

 of the orbit, crosses over the optic nerve, and penetrates 

 through the optic foramen into the cavity of the cranium, 

 where it terminates in the cavernous sinus. It may be con- 

 sidered as commencing by an anastomosis with the facial 

 vein at the internal canthus; it then receives the following 

 branches: 



