502 THE ARTERIES 



(h) The Palpebral Branches 



The palpebral branches arise either separately or by a common trunk from 

 the ophthahnir artery djiposite the pulley fur the superior oblicjue, just as the latter 

 vessel is about to divide into its terminal l)ranches. They pass, one above and 

 one below the internal tarsal ligament or tendo oculi, and then skirt along the 

 upper and lower eyelids respectively, near the free margin between the tarsal 

 cartilages and the orbicularis muscle, and form a superior and inferior palpebral 

 arch by anastomosing with the palpebral branches of the lachrymal. The up})er 

 also anastomoses with the supraorbital artery and orbital branch of the temporal 

 artery; the lower Avith the infraorbital, the angular branch of the facial, and the 

 transverse facial arteries. A branch from the lower palpebral passes with the nasal 

 duct as far as the inferior meatus. Small twigs are also given to the caruncle and 

 conjunctiva. 



(i) The Frontal Branch 



The frontal branch, the upper of the terminal branches of the ophthalmic, 

 pierces the tarsal membrane at the inner angle of the orbit, passes upAvards over 

 the frontal bone, beneath the orbicularis palpebrarum and corrugator supercilii, 

 supplies the structures in its neighbourhood, and anastomoses with its fellow of 

 the opposite side, with the supraorbital, and Avith the anterior division of the super- 

 ficial temporal artery. 



(k) The Xasal Branch 



The nasal, the loAver of the terminal branches of the ophthalmic, leaves the 

 orbit at the inner canthus by perforating the tarsal meml)rane above the tendo 

 oculi. It then descends along the dorsum of the nose, beneath the integuments; 

 and anastomoses Avith the angular and lateral nasal branches of the facial. It gives 

 off a lachrymal branch as it crosses the lachrymal sac, and a transverse nasal 

 branch as it crosses the root of the nose; the latter vessel anastomoses Avith its 

 felloAv of the opposite side. 



(6) THE POSTERIOR COMMUXICATIXG ARTERY 



The posterior communicating artery (iig. 340) is giA-en off from the internal 

 carotid just before the division of that vessel into the anterior and middle cerebral 

 arteries; occasionally it arises from the middle cerebral itself. It is as a rule a 

 slender vessel which runs backwards over the optic tract and crus cerebri along the 

 side of the uncinate convolution to join the posterior cerebral. At times, however, 

 it is of considerable size, and contributes chiefly to form the posterior cerebral, the 

 jiortion of the latter A^essel between the basilar and posterior communicating being 

 then as a rule reduced to a mere rudiment. It giA-es off the folloAving branches: — 

 (a) the uncinate, to the convolution of that name; and (6) the middle thalamic, 

 to the optic thalannis. 



(7) THE ANTERIOR CHOROID ARTERY 



The anterior choroid is a small but constant A'essel, which arises as a rule 

 from the back part of the internal carotid just external to the origin of the 

 posterior communicating. It passes backwarcls on the o])tic tract and the crus 

 cerebri, at first lying parallel and a little external to the posterior connnunicating 

 artery, and then, turning slightly outwards, dips under tlie edge of the uncinate 

 couA'oiution, and, entering the transverse fissure at the loAver end of the descending 

 cornu of the lateral ventricle, ends in the choroid plexus and su]ip]ies tlie hi])i)0- 

 campus major and corpus limbriatum. 



