Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/272

 Part lit. 228 A N A T O M Y. and the glandulous. membrane oF the pofterior nares, v/ard, and makes a third angle on the fide of the fella through the foramen fpheno-palatinum. fphenoidalis ; and again a fourth, under the clinoid apoIt is diitributed interiorly and laterally to the parts phyfis of that fella. contained in the orbit, and detaches a fmall fubaltern As it leaves the bony canal to enter the cranium, it branch through the extremity of the fuperior orbitary, fends off a branch through the fphenoidal fiffure to the or fphenoidal liiTure, which enters the cranium, and is orbit and eye, and foon afterwards another through the 1'pent upon the dura mater. foramen opticum. It fends off likewife another fubaltern branch, which Afterwards the internal carotid runs under the bafis of paffes through the. potlerior opening of the orbitary ca- the brain, to the fide of the infundibulum, where it is at a nal, and having furnifbed the maxillary Gnus and the fmall dillance from the internal carotid of the other fide, teeth, goes out by the inferior orbitary hole, and on the and there it commonly divides into two principal branches, cheek communicates with the angular artery. one anterior, and one pofterior. Tlie fecond branch runs through the canal of the low- The anterior Branch runs forward under the brain, er jaw, and being diftributed to the alveoli and teeth, firft feparating from that on the other fide, then coming goes out at the hole near the chin, and lofes itfelf in the nearer again, it unites with it by an anaftomofis, or comneighbouring mufcles. munication, in the interllice between the olfadtory nerves. The third branch runs iap between the internal and ex- Afterwards having fent off fome fmall arteries, which ternal carotids, paffes through the foramen fpinale of the accompany thefe nerves, it leaves its fellow, and divides fphenpidal bone, and is diitributed to the dura mater by into two or three. feveral ramifications. The firll of thefe branches goes to the anterior lobe The lixth anterior or internal branch, which is very of the brain; the fecond, which is fometimes double, fmall, is fpent on the mufculus maffeter. is inverted on the corpus callofum, to which it gives fome The lirlt external or pollerior branch is named arteria ramifications, as alfo to the falx of the dura mater, and occipitalis. It paffes obliquely before the internal jugu- middle lobe of the brain. The third goes to the polar vein, and having twigs to the mufculas ftylo-hyoidseus, fterior lobe of the brain. ftylo-gloffus, and digaltricus, it runs between the Ityloid The pofterior branch communicates firft of all with and maftoid apophyfes, along the maftoid groove, and the vertebral artery of the fame fide, and then divides goes to the mufcles and integuments which cover the os into feveral rami, which run between the fuperncial ciroccipitis, turning feveral times in an undulating manner, cumvolutions of the brain, and are ramified in many di£ ferent directions on.' and between thefe circumvolutions, as it afcends backwards. The fecond external branch fpreads itfelf on the out- all the way to the bottom of the fulci. ward ear, by a great many fmall twigs on each fide, fe- All thefe ramifications are covered by the pia mater, veral of which run inward, and furnilh the cartilages, in the duplicature of which they are diftributed, and form meatus auditorius, Ikin of the tympanum, and internal capillary reticular textures in great numbers ; and afterwards are loft in the inner fubftance of the brain. ear. The trunk of the external carotid afcends afterward The Subclavian arteries are two in number, one above the zygoma, paffing between the angle of the low- right, the other left; and they arife from the arch of the er jaw and parotid gland, and forms the temporal artery, aorta, on each fide of the left carotid, which commonly which divides into an anterior, middle, and pollerior lies in the middle between them ; but when both carotids go out feparately, they both lie between the fubbranch. The anterior branch of the temporal artery goes to clavte. the mufculus frontalis, communicates with the arteria The right fubclavian is larger at the begioning than angularis, and fometimes gives off a very fmall artery, the left, when it produces the right carotid; its origin which pierces the internal apophyfis of the os mate all is likewife more anterior and higher, becaufe of the obof the arch of the aorta. Both of them are di* the way to the orbit. The middle branch goes partly to liquity much in the fame manner, and therefore the the mufculus frontalis, partly to the occipitalis. The po- ftributed llerior branch goes to the occiput, and communicates with defeription of one may likewife be applied to the other. the arteria occipitalis. All thefe branches likewife fur- The right fubclavian, the longeft of the two, gives off, firft of all, fmall arteries to the mediaftinum, thynilh the integuments. / The internal carotid artery, leaving the general trunk, mus, pericardium, afpera arteria, &c. which are named thymic*, pericardia, and tracheales. is at firll a little incurvated, appearing as if either it were mediaftinum, Afterward this right fubclavian, at about? a finger’s the only branch of that trunk, or a branch of the trunk breadth from its origin, often produces the common caof the external carotid. It is fituated a little more backward than the carotis rotid of the fame fide; and at a fmall finger’s breadth externa, and generally runs up, without any ramification, from the carotid, it gives off commonly three confideras high as the lower orifice of the great canal of the apo- able branches, viz. the mammaria interna, cervicalis, phyfis petrofa of the os temporis. It enters this orifice and vertebralis, and fometimes an intercoftal artery, which goes to the firft ribs, called intercojlalis fuperior. direftly from below upward. At the end of this canal it is again incurvated from The arteria thymica communicates with the mammaria and fometimes arifes from the anterior middle below upward, and enters the cranium through a notch interna, of the fphenoidal bone. Then it bends from behind for- rpart of the common trunk of the fubclavian and carotid. TIp