OCR Text |
Show 312 MR. F. E. BEDDARD ON* THE [Nov. 3, artery gives off'several branches of varying importance as to size. The first of these is one of the smallest in size but greatest in morphological importance; it arises from where the artery has begun very definitely to bend backwards, and is directed upwards towards the dorsal side of the body. It is, in fact, the Ductus Botalli, the link between this aortic arch and the preceding one. The principal branch in point of size arises from the same side and a little further on. This closely accompanies the pulmonary artery, so closely that it is bound up in the same sheath and had to be carefully dissected away. It gives off two branches on the dorsal side and one on the ventral side. At the base of the lung this vessel abandons its close companionship with the main pulmonary trunk, and runs along a different face of the lung. This branch is not figured by Osawa. The Ductus Botalli, as has been already mentioned, joins a branch from the third vascular arch, and the conjoined vessels give off a number of twigs to the adjacent musculature, which are illustrated in the drawing submitted herewith (text-fig. 33, p. 311) *. I take it that this series of small vessels, which have been referred to as existing in all of the vascular arches, are the arteries which originally supplied the branchia. There is a final fact about the pulmonary artery, to which I desire to refer. The right pulmonary artery gives off a branch which supplies the oesophagus. I could find no corresponding branch on the left side, and indeed I do not think that one exists. I imagine that the various small branches of the pulmonary arch and of its large branch collectively represent the cutaneous trunk of the Amphibia generally. The Pulmonary vein might easily escape attention, as it is not at all apparent on a dissection. It lies in fact directly above the vena cava inferior, and being of much smaller dimensions, it is completely covered by that vein when the animal is dissected from the ventral surface. The two pulmonary veins join each other just within the pericardium, where they form a tolerably Avide trunk. The common pulmonary vein increases in diameter as it passes along the sinus venosus, and finally opens into the smaller division of the auricle. There is thus at least a partial separation of arterial and venous blood in the heart. Intercostal Arteries and Veins.-The very deep fold of peritoneum which ties down the aorta to the dorsal parietes enables me to see clearly the course of the intercostal arteries and of certain intercostal veins, which are presumably branches of the portal system in the abdominal region. Of the arteries I counted seven, four of which are arranged in pairs, while the three remaining arteries are not so disposed. They arise from the aorta, however, definitely on one side or the other; they are not median in origin. Furthermore, the points of entrance into the thickness of the parietes are not median; they are on one side or the other, and in the case of the paired arteries they enter the * Prof. Osawa represents nothing more than a simple transverse Ductus Botalli uniting the arteries in question. |