THE ORBIT 255 



the eyeball, where they form an arterial circle under the con- 

 junctiva. Finally, they pierce the sclera immediately posterior 

 to the cornea. 



Arteria Supraorbitalis. The supra-orbital artery accom- 

 panies the supra-orbital nerve to the forehead, where it was 

 dissected at a previous stage (p. 47). 



Artericz Ethmoidaks. There are two ethmoidal branches, 

 an anterior and a posterior ; they pass through the anterior 

 and posterior ethmoidal foramina in the medial wall of the 

 orbit. The posterior ethmoidal artery supplies the mucous 

 lining of the posterior ethmoidal cells, and sends twigs to the 

 upper part of the nose. The anterior ethmoidal artery is 

 a larger branch. It runs in company with the anterior 

 ethmoidal nerve, and gives off minute twigs at each stage of 

 its course. Thus, in the anterior ethmoidal foramen, it gives 

 branches to the mucous lining of the anterior ethmoidal cells 

 and the frontal sinus during its short sojourn in the cranial 

 cavity it gives off a small anterior meningeal artery ; in the 

 nasal cavity, it gives twigs to the mucous membrane. Its 

 terminal branch appears on the face and supplies the side of 

 the nose. 



Arteria Dorsalis Nasi. The dorsal artery of the nose is 

 distributed at the root of the nose, and anastomoses with 

 the angular branch of the external maxillary artery. 



Arteria Frontalis. The frontal artery accompanies the 

 supra -trochlear nerve to the forehead, where it has been 

 dissected already (p. 47). 



Venae Ophthalmicse. As a general rule there are two 

 ophthalmic veins, superior and inferior. The superior 

 ophthalmic vein is the larger of the two and it accompanies 

 the artery. It takes origin at the root of the nose, where 

 it communicates with the angular vein. The inferior 

 ophthalmic vein lies below the level of the optic nerve, and 

 it is brought into communication with the pterygoid venous 

 plexus by an offset which passes through the inferior orbital 

 fissure. The two ophthalmic veins receive numerous tribu- 

 taries during their course through the orbit ; finally they 

 pass between the two heads of the lateral rectus muscle, and 

 through the superior orbital fissure, to open into the cavernous 

 sinus, either separately or by a common trunk. 



Musculi Recti et Obliqui Oculi. Associated with the 

 origins of the recti muscles of the eyeball are two tendinous 



