638 MH. c. H. o'donoguue on the 



III. The anterior branch (Ramus cranialis, Hofmann) runs 

 forward along the side of the pituitary fossa and unites with the 

 similar vessel from the other side under the bases of the optic 

 nerves immediately in front of the chiasma. By the union of 

 the two anterior and the two posterior bi'anches of the cerebral 

 carotids a complete arterial ling, the circle of Willis (circulus 

 nrteriosus cerebralis, Hofmann) is formed around the pituitary 

 fossa. During its course this anterior branch gives off: — 



A. A Median Cerebral Artery (Art. cerebri media, Hofmann), 



which is a large vessel i-unning round to the dorsal side 

 of the brain and supplying the anterior end of the hemi- 

 sphei'es and the olfactory lobes. 



B. An Ojjhthalmic Artei-y (Art. ophthalmica, Hofmann), which 



is given off immediately before the two anterior branches 

 of the cei'ebral carotids unite to form the circle of Willis. 

 This passes out of the skull with the optic nerve, and 

 immediately on reaching the orbit anastomoses with a 

 branch of the facial carotid. 



The Olfactory Artery * (Art. olfactoria, Schlemm) arises from 

 the mid-point of the anastomosis of the two anterior branches of 

 the cerebral carotids and runs forward iti the skull in the furrow 

 between the two olfactoiy lobes, to which it sends branches. At 

 the anterior end of the lobes it gives off two symmetrical branches. 

 Each of these again divides into two (Aa. etlimoidales, Rathke ; 

 Aa. bulbi olfactorii mediales, Hofmann), which pass out of the 

 skull with the olfactory nerve to ramify over the olfactoiy 

 membrane. The main trunk then recui-ves dorsally and runs back 

 in the fissure between the two hemis]3heres, to which it sends 

 numerous small branches, and near the pineal body anastomoses 

 on each side with a branch of the anterior division of the median 

 branch of the cerebral arter3^ 



Tie Inferior Spinal Artery (Art. spinalis inferior, Rathke ; 

 Tractus spinalis ventralis, Hofmann) is situated just below the 

 ventral fissure of the spinal colxl, and runs in a fairly straight line 

 caudally from the anastomosis between the right and left first 

 spinal arteries at the posterior end of the basilar artery. On its 

 course it gives off branches to the spinal cord, some of which pass 

 around to the dorsal side and others enter the ventral fissure, and 

 it also receives the paired spinal arteries which come in through 

 the vertebral column at the points of exit of the spinal nerves. 

 In some places where a pair of such arteries enter it, the infeiior 

 spinal artery splits into a diamond-shaped loop. 



The Facial Carotid (Oarotis facialis, Rathke) takes a fairly 

 sti'aight course forward through the temporal fossa close to the 

 infra-maxillary branch of the trigeminal nerve to the orbit. 

 Here it passes under the post-fi'ontal bone into the orbit and 



* This Hvtcrv is doulilo I'ov tlir irventiT fiivt of its lcii2;tli in Pi/fJ/nii moJv.rnx. 

 V.cd&.n-d (6). 



