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Show 1894.] ANATOMY OF ORNITHORHYNCHUS. 713 This divides at once into the following branches proceeding from wdthout inwards:- A slender branch to bladder. This is Hyrtl's cystic artery. A large branch, which runs downwards and backwards ; leaves pelvis beneath symphysis pubes; runs down on the side of the rectum, and is distributed to the penis and to Cowper's gland. This may represent internal pudic; it gives off branches to bladder, rectum, and an artery, which divides into a pencil of fine vessels and passes to the under surface and side of middle of tail. This artery Hyrtl speaks of as the common pudendal. A pencil of fine vessels, four in number, which descend into the pelvis parallel to each other, soon subdivide, and passing from thence are eventually distributed to the sides of the tail. This pencil has divided into a set of ten or twelve fine vessels at the side of the anterior part of caudal region. The innermost of the three trunk branches divides at once into three vessels ; these descend into pelvis parallel to each other, and emerging from thence are distributed to the gluteal region; the largest of the three passes to the back of the thigh. These arteries represent gluteal and sciatic. The central caudal artery descends in the middle line to tip of tail. The whole arrangement is repeated on the opposite side. Branches of the Trunk Aorta. The only branches given off from thoracic trunk are the intercostal arteries. These are nine in number on each side. The first supplies the third and fourth spaces, running along the line of the fourth rib and giving off branches anteriorly and posteriorly to third and fourth spaces. The fifth to the twelfth intercostal intervals are supplied by the second, third, fourth, fifth, sixth, seventh, and eighth arteries. The thirteenth, fourteenth, and fifteenth intervals are supplied by the ninth aortic intercostal. The sixteenth interval is supplied by the first and second lumbar arteries. The upper two spaces are supplied by a superior intercostal. There are five lumbar arteries. They come off by a common trunk which immediately divides into the arteries of opposite sides ; the first and second supply the last intercostal spaces; the others are quite below the ribs ; the last one passes backwards to the posterior surface of the sacrum and traverses the sacral arcade of Howes l. Visceral Branches. There is a cceliac or coelio-mesenteric axis dividing into gastro-hepatic, splenic, and superior mesenteric. They are distributed to the structures indicated by their names. Benal arteries.-There are two short renal arteries, which are not very large. Midway between the renal and the division of the aorta is a slender spermatic artery which is extremely tortuous. i 'Journal of Anatomy and Physiology,' vol. vii., n. s., 1892-93. |