THE HEAD AND NECK ll6t 



passes through the anterior ethmoidal canal along with the nasal 

 nerve, and enters the anterior fossa of the base of the skull. Here 

 it crosses the cribriform plate of the ethmoid bone to the nasal slit by 

 the side of the crista galli. It then descends through this slit, still 

 in company with the nasal nerve, traverses the nasal groove on the 

 posterior surface of the nasal bone, and finally emerges between 

 the lower border of the nasal bone and the upper lateral nasal 

 cartilage to the tip of the nose. Its branches supply the dura matei 

 in the anterior cranial fossa, the mucous membrane of the anterior 

 ethmoidal cells and corresponding frontal sinus, the mucous 

 membrane of the upper and anterior parts of the nasal fossa, and 

 the skin of the tip of the nose. 



The palpebral arteries (internal) are two in number, superior and 

 inferior, and are distributed to the eyelids. They arise, separately 

 or conjointly, from the ophthalmic close to the pulley of the superior 

 oblique muscle, and each takes an outward course in the correspond- 

 ing eyelid. They anastomose with the superior and inferior palpe- 

 bral branches of the lachrjTnal artery, thus forming arterial arches. 



The nasal artery is one of the terminal branches of the ophthalmic. 

 It emerges from the orbit above the internal tarsal ligament, and is 

 distributed to the upper part of the side of the nose in the region 

 of the root, where it anastomoses with the angular and lateral nasal 

 branches of the facial artery. 



The frontal artery is the other terminal branch of the ophthalmic. 

 It emerges from the orbit at the inner angle, and then ascends to 

 the frontal region, along with the supratrochlear nerve, to be dis- 

 tributed to the integument by the side of the median line. It 

 anastomoses with the supra-orbital artery and its fellow of the 

 opposite side. 



Ophthalmic Veins. — ^These are two in number, superior and 

 inferior. The superior ophthalmic vein, of large size, commences at 

 the inner angle of the orbit, where it communicates freely with the 

 angular vein, which is the commencement of the facial vein. It 

 accompanies the ophthalmic artery, passing outwards and back- 

 wards over the optic nerve. Having reached the inner end of the 

 sphenoidal fissure, the vessel passes between the two heads of the 

 external rectus muscle, and through the fissure, after which it opens 

 into the anterior part of the cavernous sinus. Its tributaries 

 correspond for the most part to the branches of the ophthalmic 

 artery. It does not, however, receive the frontal vein, nor the 

 supra-orbital vein, but it is in communication with the latter by 

 means of a small branch through the supra-orbital foramen. The 

 inferior ophthalmic vein arises in connection with the lower posterior 

 ciliary and lower muscular veins. It passes backwards along the 

 floor of the orbit, and, as a rule, it joins the superior ophthalmic 

 vein before that vessel passes between the two heads of the external 

 rectus, thus giving rise to what is known as the common ophthalmic 

 vein. It may, however, leave the orbit separately and open inde- 

 pendently into the anterior part of the cavernous sinus. It com- 



