344 HEAD AND NECK 



Arterue Ethmoidales. There are two ethmoidal branches, 

 an anterior and a posterior ; they pass through the anterior 

 and posterior ethmoidal foramina on the medial wall of the 

 orbit. The arteria ethmoidalis posterior supplies the mucous 

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

 upper part Df the nose. The arteria ethmoidalis anterior 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 arteria meningea anterior ; 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. This accompanies the supra-trochlear 

 nerve to the forehead, where it has been dissected already 



(P- IS?)- 



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 Oculi. The four straight muscles of the 

 eyeball diverge from the apex of the orbit. They form the 

 sides of a four-sided or pyramidal space in which are en- 

 closed the optic nerve and the greater part of the globe of 

 the eye. The rectus superior, which has been reflected, has 

 been studied already. The rectus medialis springs from the 

 medial side of the optic foramen, and the rectus inferior takes 

 origin from a fibrous band which bounds the medial end of the 



