904 A N A T M Y [VASCULAR the vertebras above, lies in a groove on the arch of the atlas, and enters the skull through the foramen magnum, where it joins its fellow to form the basilar artery ; it gives off muscular branches to the deep muscles of the neck, spinal branches to the spinal cord, meningeal branches to the dura mater, and an inferior cerebellar branch to the under surface of the cerebellum. The basilar artery, formed by the junction of the two vertebrals, extends from the lower to the upper border of the pons Varolii ; it gives off collaterally transverse, branches to the pons, auditory branches which accompany the portio mollis to the internal ear, inferior cerebellar brandies to the under surface of the cerebellum, whilst it breaks up into four terminal branches, viz., two superior cerebellar to the upper surface of the cerebellum, and two posterior cerebral which supply the tentorial aspect of the temporo-sphenoidal lobes, the occi pital lobes, and the posterior convolutions of the parietal lobes, b, Thyroid axis, which immediately divides into the inferior thyroid, the supra-scapular, and the transverse cervical branches ; the inferior thyroid supplies the thyroid body, and gives off an ascending cervical branch to the muscles of the neck ; the supra-scapidar supplies the mus cles on the dorsum scapulae ; the transverse cervical sup plies the trapezius and the muscles attached to the vertebral border of the scapula, c, Internal mammary, supplies the anterior surface of the walls of the chest and abdomen, and the upper surface of the diaphragm, d, Siq^erior inter costal supplies the first intercostal space, and by its deep cervical branch the deep muscles of the back of the neck. The axillary artery supplies long and short thoracic branches to the wall of the chest and the pectoral muscles ; an alar thoracic branch to the fat and glands of the axilla ; an acromial thoracic to the parts about the acromion ; anterior and posterior circumflex branches to the shoulder joint and deltoid muscle ; a subscapular branch to the muscles of the posterior fold of the axilla. The brachial artery supplies muscular branches to the muscles of the upper arm ; a nutrient branch to the humerus ; superior and inferior profunda branches and an anastomotic to the muscles of the upper arm and the region of the elbow joint. The ulnar artery extends down the ulnar side of the front of the fore-arm to the palm of the hand, where it curves outwards towards the thumb, and anastomoses with the superficial volar and radial index branches of the radial artery to form the superficial palmar arterial arch. In the fore-arm the ulnar gives off the interosseous arteries, which supply the muscles of the fore-arm and give nutrient branches to the bones ; two recurrent branches to the region of the elbow ; carpal branches to the wrist joint : in the hand it gives a deep branch to the deep muscles of the hand, and from the superficial arch arise digital branches to the sides of the little, ring, and middle fingers, and the ulnar border of the index finger. The radial artery extends down the radial side of the front of the fore-arm, turns round the outer side of the wrist to the back of the hand, passes between the 1st and 2d metacarpal bones to the palm, where it joins the deep branch of the ulnar, and forms the deep palmar arterial arch. In the fore-arm it gives off a recurrent branch to the elbow joint ; carpal branches to the wrist joint ; and mus cular branches, one of which, named superflcialis voles, supplies the muscles of the thumb and joins the ulnar artery : in the hand it gives off a digital branch to the thumb, and one to the radial side of the index, interosseous branches to the interosseous muscles, perforating branches to the back of the hand, and recurrent branches to the wrist. The common carotid artery runs up the neck by the side of the windpipe, and on a level with the upper border of the thyroid cartilage divides into the internal and external carotid arteries. The internal carotid artery ascends through the carotid canal in the temporal bone into the cranial cavity. It gives off an ophthalmic branch to the eyeball and other contents of the orbit, and then divides into the anterior and middle cerebral arteries. The middle cerebral artery extends outwards into the Sylvian fissure, and supplies the island of Reil, the orbital part, and the outer face of the frontal lobe, the parietal lobe, and the temporo-sphe noidal lobe ; it also gives a choroid branch to the choroid plexus of the velum interpositum. The anterior cerebral artery supplies the inner face of the hemisphere from the anterior end of the frontal lobe as far back as the internal parieto-occipital fissure. At the base of the brain not only do the two internal carotids anastomose with each other through the anterior communicating artery, which passes between their anterior cerebral branches, but the internal carotid on each side anastomoses with the posterior cerebral branch of the basilar, by a posterior communicating artery. In this manner a vascular circle, the circle of Willis, ia formed, which permits of freedom of the arterial circula tion by the anastomoses between arteries not only on the same side, but on opposite sides of the mesial plane. The vertebral and internal carotid arteries, which are the arteries of supply for the brain, are distinguished by lying at some depth from the surface in their course to the organ, by having curves or twists in their course, whereby the force of the flow of blood is retarded, and by the absence of large collateral branches. Further, as the ophthalmic artery is a branch of the internal carotid, the circulation in the eyeball is in sympathy with that in the brain. The external carotid artery ascends through the upper part of the side of the neck, and behind the lower jaw into the parotid gland, where it divides into the internal maxillary and temporal branches. This artery gives off the following branches : a, Superior thyroid to the larynx and thyroid body ; b, Lingual to the muscles and mucous membrane of the tongue, and to the sublingual gland ; c, Facial to the face, palate, tonsil, and sub -maxillary gland ; d, Occipital to the sterno-mastoid muscle and back of the scalp ; e, Posterior auricular to the back of the ear and the adjacent part of the scalp ; /, Superficial temporal to the scalp in front of the ear, and by its transverse facial branch to the back part of the face ; g, Internal maxillary, giving muscular branches to the muscles of mastication, meningeal branches to the dura mater, dental branches to the teeth, and other branches to the nose, palate, and tympanum ; hi Ascending pharyngeal, which gives branches to the pharynx, palate, and tonsils. . The common iliac artery, after a short course, divides Iliac into the internal and external iliac arteries. The internal system. iliac enters the pelvis and divides into branches for the supply of the pelvic walls and viscera, including the organs of generation, and for the great muscles of the buttock. The external iliac descends behind Poupart s ligament into the thigh, where it takes the name of femoral artery. The femoral descends along the front and inner surface of the thigh, gives off a profunda or deep branch, which, by its circumflex and perforating branches, supplies the numerous muscles of the thigh ; most of these extend to the back of the limb to carry blood to the muscles situated there. Tho femoral artery then runs to the back of the limb in the ham, vhere it is called popliteal artery. The popliteal divides into two branches, of which one, called anterior tib tal, passes between the bones to the front of the leg, and then downwards to the upper surface of the foot ; the other, posterior tibial, continues down the back of the leg to the sole of the foot, and divides into the internal and external
plantar arteries ; branches proceed from the external plan-
