x.] THE CIRCULATING SYSTEM. 413 



stylo-mastoid foramen) to the tympanum. The external 

 carotid then continues on, assuming the name of internal 

 maxillary, and enters the spheno-maxillary fossa. 



It gives off a number of branches, and amongst them a small 

 one called the tympanic artery, which ascends through the 

 fissura Glasseri to the tympanum, and there unites (or, as it 

 is termed, anastomoses] with the posterior auricular ; also the 

 vidian, which passes back through the root of the pterygoid, 

 and some branches to muscles. It then ends by dividing 

 into the descending palatine and the nasal arteries. Of these 

 two, the former descends the posterior palatine canal along 

 with the palatine nerve, runs along the palate and enters the 

 anterior palatine foramen where it anastomoses with the nasal 

 artery. The nasal artery enters the nose through the spheno- 

 palatine foramen (in company with the nasal nerve), sends 

 twigs to the ethmoid, and, skirting the nasal septum, descends 

 the anterior palatine canal to anastomose with the descending 

 palatine as just mentioned. 



The internal carotid transverses the petrous part of the 

 temporal bone (as already noticed in the Lesson on the Skull), 

 and, ascending beside the basi-sphenoid, anastomoses with its 

 fellow of the opposite side at the pituitary fossa. While 

 ascending the carotid canal of the petrous bone it gives off 

 a small branch which anastomoses with the tympanic, vidian, 

 and posterior auricular arteries. It terminates as the oph- 

 thalmic artery, which, entering the orbit by the optic foramen, 

 skirts the inner wall of the orbit and distributes small branches 

 in various directions. 



The artery of each pectoral limb is termed the subclavian, 

 and springs on the left direct from the aortic arch, but on the 

 right from the innominate artery. 



Each subclavian gives off an artery termed "vertebral, 

 which ascends through the perforations of the cervical trans- 

 verse processes, and, entering the skull through the foramen 

 magnum, unites with its fellow to form the basilar artery, 

 which latter runs along the upper surface of the basi- occipital, 

 gives off branches to the brain, divides, and anastomoses on 

 each side with the internal carotid. 



The subclavian gives off certain other branches, and then 

 passes out of the trunk at the arm-pit as the axillary artery. 

 It descends the arm on its inner side, between the biceps 

 and the triceps muscles, and is then called brachial. At the 

 elbow it sinks between the pronator teres and supinator 

 longus, and bifurcates into the radial and ulnar arteries. 



