Infi,g.134, a is the trunk of the coeliac artery; in that of the superior and inferior mesenteric arteries; c is the capsular artery of the left side; d, d, the renal arteries ; e the spermatic artery, of which the left branch is shown continued to the left ovarium q, which, with the uterus r, vagina s, and bladder t, is drawn to the rightside; the spermatic arteries arise close together but separately in the male Vulpine Phalanger: j is the external iliac, corresponding with the com mon iliac in placental Mainmalia, and with the femoral artery in Birds, (see Vol. i. p. 337, figs. 170, 23 ;) below these are given off h, the arteries corresponding with the ischiadic ar teries in Birds, (Vol. i. p. 337, fig. 170, 26,) and with the internal iliacs in Mammalia; [they are represented of too small a size in the cut]; k is the femoral artery ; 1 the ex ternal, in the internal branch ; i is the sacro median or caudal artery, which is protected in its course along the tail by the ham apophysial or chevron-like processes of the caudal vertebra. This artery of course cor responds in size with the developement and functional importance of the tail, and must be rudimentary in the tail-less or nearly tail-less Marsupials, such as the Cliceropus, Koala, and Wombat.
With respect to the veins of the Marsupials it may here be noticed that the iliac veins combine to form the trunk of the abdominal eava, as in the rest of the Mammalia, without conveying any part of their blood to the kid neys : in the Kangaroo they both pass on the central aspect of the iliac arteries. The renal veins, in like manner, directly communicate with the abdominal cava, and do not contri bute any share in the formation of the portal vein. This great secerning trunk of the hepatic organ presents the strictly mammalian condi tion, being formed by the reunion of the gastric, intestinal, pancreatic, and splenic veins. It is in the chest that we first meet with decided traces of the oviparous type of structure in the venous system of the Marsupialia. The primi tive veins of the animal system of organs, commonly called 4 azygos,' retain their original separation and symmetry ; the left azygos' bends over the left bronchus to communicate with the left anterior cava, and the right azy gos over the right bronchus to join the right anterior cava. The left anterior cava commonly receives also the coronary vein of the heart : the termination of this and the two other venous trunks in the right auricle has already been noticed.
Respiratory organs.—In the condition and structure of the respiratory organs all the Mar supial species adhere to the Mammalian type ; the only tendency to the Ovipara is in the entireness of the tracheal rings in certain spe cies. In the Phalangista fuliginosa, where I counted twenty-nine rings, the first four-and twenty were entire ; below these they were divided posteriorly, the interspace growing wider to the twenty-ninth ring. In the Dasy
liras macrurus the rings of the trachea are twenty-three in number, and are incomplete or rather ununited behind. In the Perameles the tracheal rings are divided posteriorly by a fis sure. In no species have I found the trachea divided near the larynx into two long bronchia, as in the Rodent genus Helamys, nor convo luted in the chest as in the Edentate Sloth, both of which modifications are more striking ap proximations to the oviparous type of structure than the entire rings above-mentioned.
The lungs present the most simple form in the Wombat, in which they consist of a single lobe on both the right and left sides, with a small lobulus azygos extending from the right lung to the interspace between the heart and diaphragm.
In the Macropus major I found the right lung with two notches on the anterior margin, and the left lung undivided. In the Macropus Parryi both lungs had one or two notches. In another Kangaroo I found the right lung divided into four lobes, the left into two. The azygos lobe is large in consequence of the length of the chest in the Kangaroos, and the distance of the heart from the diaphragm : it is three-sided, one side convex, the second con cave and applied to the pericardium, the third side concave, and in contact with the dia phragm.
In the Potoroo the left lung is unilobate with a fissure on the anterior or upper edge ; the right lung has two or three deep fissures. The azygos lobe is elongated, pointed, and triedral, as in the Kangaroo.
In the Petaurists and I'halangers the right lung is trilobate, the left bilobate ; there is also a lobulus azygos. The Koala has the lungs similarly divided, and not simple as in the Wombat.
In the Opossums, Dasyures, and Perameles the right lung is usually trilobate, (bilobate in Didelphys braehyurn,) and with the usual azygos appendage : the left lung is commonly divided into two, but is sometimes entire, as in the Peranneles and Didelph. braehyura. In all the Marsupials the right lung is the largest, owing to the oblique inclination of the heart to the left side.
The thyroid glands are two disunited bodies n the Dasyures ; they were each the size of a horse-bean in the Das. ntaerurus. They were of the same size in a Phalangista faliginosa, but were united by a filamentary strip passing between their lower extremity, across the first tracheal ring. In the Koala, the thyroid gland is situated lower down extending from the fourth to the ninth or tenth tracheal ring. In the Wombat I found the thyroid glands two elongated bodies of a dark colour reaching from the thyroid cartilage to the seventh tracheal ring on each side.