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to the internal ear, inferior cerebellar branches 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 and mesial aspects of the temporo-sphenoidal lobes, the occipital 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-scapular supplies the muscles on the dorsum scapulae; the transverse cervical supplies 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) Superior intercostal supplies the first intercostal space, and by its deep cervical branch the deep muscles of the back of the neck.

The axillary artery supplies thoracic branches to the wall of the chest, the pectoral muscles, and the fat and glands of the axilla; an acromio-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 outward toward the thumb, and anastomoses with the superficial volar or other branch of the radial artery to form the superficial palmar 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 2nd metacarpal bones to the palm, where it joins the deep branch of the ulnar, and forms the deep palmar arch. In the fore-arm it gives off a recurrent branch to the elbow joint; carpal branches to the wrist joint; and muscular branches, one of which, named superficial volar, supplies the muscle of the thumb and joins the ulnar artery; in the hand it gives off a 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 branches of the aorta which supply the viscera of the thorax are the coronary, the oesophageal, the bronchial and the pericardiac. The coronary arteries, two in number, are the first branches of the aorta, and arise opposite the anterior and left Visceral branches. posterior segments of the semilunar valve, from the wall of the aorta, where it dilates into the sinuses of Valsalva. They supply the tissue of the heart.

The oesophageal, bronchial and pericardiac branches are sufficiently described by their names.

The branches of the aorta which supply the viscera of the abdomen arise either singly or in pairs. The single arteries are the coeliac axis, the superior mesenteric, and the inferior mesenteric, which arise from the front of the aorta; the pairs are the capsular, the two renal, and the two spermatic or ovarian, which arise from its sides. The single arteries supply viscera which are either completely or almost completely invested by the peritoneum, and the veins corresponding to them are the roots of the vena portae. The pairs of arteries supply viscera developed behind the peritoneum, and the veins corresponding to them are rootlets of the inferior vena cava.

The coeliac axis is a thick, short artery, which almost immediately divides into the gastric, hepatic and splenic branches. The gastric gives off oesophageal branches and then runs along the lesser curvature of the stomach. The hepatic artery ends in the substance of the liver; but gives off a cystic branch to the gall bladder, a pyloric branch to the stomach, a gastro-duodenal branch, which divides into a superior pancreatico-duodenal for the pancreas and duodenum, and a right gastro-epiploic for the stomach and omentum. The splenic artery ends in the substance of the spleen; but gives off pancreatic branches to the pancreas, vasa brevia to the left end of the stomach, and a left gastro-epiploic to the stomach and omentum.

The superior mesenteric artery gives off an inferior pancreatico-duodenal branch to the pancreas and duodenum; about twelve intestinal branches to the small intestines, which form in the substance of the mesentery a series of arches before they end in the wall of the intestines; an ileocolic branch to the end of the ileum, the caecum, and beginning of the colon; a right colic branch to the ascending colon; and a middle colic branch to the transverse colon.

The inferior mesenteric artery gives off a left colic branch to the descending colon, a sigmoid branch to the iliac and pelvic colon, and ends in the superior haemorrhoidal artery, which supplies the rectum. The arteries which supply the coats of the alimentary tube from the oesophagus to the rectum anastomose freely with each other in the wall of the tube, or in its mesenteric attachment, and the anastomoses are usually by the formation of arches or loops between adjacent branches.

The capsular arteries, small in size, run outward from the aorta to end in the supra-renal capsules.

The renal arteries pass one to each kidney, in which they for the most part end, but in the substance of the organ they give off small perforating branches, which pierce the capsule of the kidney, and are distributed in the surrounding fat. Additional renal arteries are fairly common.

The spermatic arteries are two long slender arteries, which descend, one in each spermatic cord, into the scrotum to supply the testicle. The corresponding ovarian arteries in the female do not leave the abdomen.

The branches of the aorta which supply the walls of the thorax, abdomen and pelvis, are the intercostal, the Parietal branches. lumbar, the phrenic, and the middle sacral.

1911 Britannica - intercostal arteries.png
Fig. 1.—Diagram of a pair
of intercostal arteries.
Ao, The aorta transversely divided, giving off
at each side an intercostal artery.
PB, The posterior or dorsal branch.
AB, The anterior or proper intercostal branch.
IM, A transverse section through the internal
mammary artery.

The intercostal arteries arise from the back of the thoracic aorta, and are usually nine pairs. They run round the sides of the vertebral bodies as far as the commencement of the intercostal spaces, where each divides into a dorsal and a proper intercostal branch; the dorsal branch passes to the back of the thorax to supply the deep muscles of the spine; the proper intercostal branch (AB.) runs outward in the intercostal space to supply its muscles, and the lower pairs of intercostals also give branches to the diaphragm and wall of the abdomen. Below the last rib a subcostal artery runs.

The lumbar arteries arise from the back of the abdominal aorta, and are usually four pairs. They run round the sides of the lumbar vertebrae, and divide into a dorsal branch which supplies the deep muscles of the back of the loins, and an abdominal branch which runs outward to supply the wall of the abdomen. The distribution of the lumbar and intercostal arteries exhibits a transversely segmented arrangement of the vascular system, like the transversely segmented arrangement of the bones, muscles and nerves met with in these localities, but more especially in the thoracic region.

The phrenic arteries, two in number, pass to supply the under surface of the diaphragm.

The middle sacral artery, as it runs down the front of the sacrum, gives branches to the back of the pelvic wall.

Injections made by Sir W. Turner have shown that, both in the thoracic and abdominal cavities, slender anastomosing communications exist between the visceral and parietal branches.

The arteries to the pelvis and hind limbs begin at the bifurcation of the aorta into the two common iliacs.

The common iliac artery, after a short course, divides into the internal and external iliac arteries. The internal 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 Iliac
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. The femoral artery then runs to the back of the limb in the ham, where it is called popliteal artery. The popliteal divides into two branches, of which one, called anterior tibial, passes between the bones to the front of the leg, and then downward 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 plantar artery to the sides of the toes, and constitute the digital arteries. From the large arterial trunks in the leg many branches proceed, to carry blood to the different structures in the limb.

The wall of an artery consists of several coats (see fig. 2). The outermost is the tunica adventitia, composed of connective tissue; immediately internal to this is the yellow elastic coat; within this again the muscular coat, formed of involuntary Structure
muscular tissue, the contractile fibre-cells of which are for the most part arranged transversely to the long axis of the artery; in the larger arteries the elastic coat is much thicker than the muscular, but in the smaller the muscular coat is relatively strong; the vaso-motor nerves terminate in the muscular coat. In the first part of the aorta, pulmonary artery and arteries of the retina there is no muscular coat. Internal to the muscular coat is the elastic fenestrated coat, formed of a smooth elastic membrane