904 THE VASCULAE SYSTEM. 



the lateral wall of the nasal cavity. The anterior ethmoidal artery passes through the anterior 

 ethmoidal canal with the anterior ethmoidal nerve, enters the anterior fossa of the skull and 

 crosses the lamina cribrosa of the ethmoid to the nasal slit, through which it reaches the 

 nasal cavity where it descends, with the external branch of the nasal nerve, in a groove on the 

 posterior surface of the nasal bone, and, finally, passes between the lateral cartilage and the 

 lower border of the nasal bone to the tip of the nose. It supplies branches to the membranes 

 of the brain in the anterior cranial fossa as well as to the anterior ethmoidal cells, the frontal 

 sinus, the anterior and upper part of the nasal rnuco- periosteum, and the skin on the dorsum 

 of the nose. 



(h) Palpebral branches, upper and lower, are given off near the termination of the 

 ophthalmic. They are distributed to the upper and lower eyelids, and they anastomose with the 

 lacrimal, supra-orbital, and infra-orbital arteries. 



(i) The dorsal nasal terminal branch passes out of the orbit above the medial tarsal 

 ligament. It pierces the palpebral fascia, and terminates on the side of the nose by anastomosing 

 with the angular branch of the external maxillary artery. 



(j) The frontal terminal branch pierces the palpebral fascia at the upper and medial 

 part of the orbit, and ascends, with the supra-trochlear nerve, in the superficial fascia of the 

 anterior and medial part of the scalp, anastomosing with its fellow of the opposite side and 

 with the supra-orbital artery. 



(6) The posterior communicating artery arises from the internal carotid near its 

 termination. It runs backwards, below the optic tract and anterior to the pedunculus 

 cerebri, and, passing above the oculomotor nerve, joins the posterior cerebral artery forming 

 part of the circulus arteriosus (Willis). It gives branches to the optic chiasma, the optic 

 tract, the pedunculus cerebri, the interpeduncular region, the internal capsule, and the optic 

 thalamus. The posterior communicating artery varies much in size ; it may be small 

 on one or both sides, sometimes it is very large on one side ; occasionally it replaces 

 the posterior cerebral artery, and it sometimes arises from the middle cerebral artery. 



(7) The chorioidal is a small branch, which also arises near the termination of the 

 internal carotid ; it passes backwards and laterally, between the pedunculus cerebri and 

 the uncus, to the lower and anterior part of the chorioidal fissure which it enters, and 

 it terminates in the chorioidal plexus in the inferior cornu of the lateral ventricle. 

 It supplies the optic tract, the pedunculus cerebri, the uncus, the posterior part of the 

 internal capsule, the tail of the caudate nucleus, part of the lentiform nucleus, and the 

 amygdaloid nucleus. 



(8) Arteria Cerebri Anterior. The anterior cerebral artery is the smaller 

 of the two terminal branches of the internal carotid. It passes forwards and 

 medially, above the optic chiasma and in front of the lamina terminalis,. to the 

 commencement of the longitudinal fissure ; there it turns round the genu of the 

 corpus callosum, and runs backwards to the parietal lobe of the brain. At 

 the commencement of the longitudinal fissure it is closely connected with its 

 fellow of the opposite side by a wide but short anterior communicating artery, 

 and in the remainder of its course it is closely accompanied by its fellow artery 

 of the opposite side. 



Branches. Branches of all the cerebral arteries are distributed both to the basal 

 ganglionic masses of the brain and to the cerebral cortex ; they therefore form two distinct 

 groups which do not communicate with one another (a) central or basal ; (b) cortical. 



The branches of the anterior cerebral include : 



(a) Central or basal branches. The antero-medial basal arteries, a small group of 

 vessels, constitute the basal branches of the anterior cerebral artery ; they pass upwards 

 into the base of the brain, in front of the optic chiasma, and supply the rostrum of 

 the corpus callosum, the lamina terminalis, the head of the caudate nucleus, the anterior 

 part of the lentiform nucleus and internal capsule, the columns of the fornix, the septum 

 pellucidium, and the anterior commissure. 



(b) Cortical branches. (b l ) Medial orbital, one or more small branches which 

 supply the medial orbital convolution, the gyrus rectus, and the olfactory lobe. 



(6 2 ) Anterior medial frontal, one or more branches which are distributed to the an- 

 terior and lower part of the medial surface of the superior frontal gyrus, and to the anterioi 

 portions of the superior and middle frontal gyri on the lateral surface of the hemisphere. 



(6 8 ) An intermediate medial frontal is distributed to the posterior part of the media 

 lateral surfaces of the superior frontal gyrus and to the upper parts of the anterior anc 

 posterior central gyri. 



(6 4 ) The posterior medial frontal runs backwards to the preecimeus. It supplie 

 the corpus callosum, the praecuneus, and the upper part of the superior parietal lobule. 



