MARSUPIALIA. 



(h) alone hag a separate origin. The common 

 carotid in the Kangaroo gives off the thyroid 

 artery, and afterwards divides opposite the 

 transverse process of the atlas into the external 

 and internal carotids. The internal carotid 

 describes a sharp curve at its origin, and passes 

 along the groove between the occipital condyle 

 and the exoccipital process to the foramen ca- 

 roticum. The vertebral arteries are given off 

 by the subclavians, and pass to the skull, as 

 usual, through the vertebral foramina of the 

 cervical transverse processes. They unite be- 

 neath the medulla oblongata to form the basilar 

 artery, which sends oft" at right angles to the 

 cerebellum two branches as large as itself: it 

 divides opposite the anterior margin of the 

 pons Varolii, and the diverging branches are 

 connected by two straight transverse canals, 

 before they anastomose with the internal caro- 

 tids to form the circle of Willis. No pecu- 

 liarly marsupial condition occurs in the distri- 

 bution of the other arteries of the head, or 

 those of the neck, the chest, and anterior ex- 

 tremities; but I may observe that in the Koala, 

 Wombat, Kangaroos, Potoroos, most Phalan- 

 gers, ( Phul. Cookii is an exception,) most Pe- 

 taurists, (Pet. Sciureus is an exception,) the 

 Opossums, Bandicoots, and Phascogales, the 

 brachial artery perforates the internal condyle 

 of the humerus; it passes over that condyle, 

 impressing it with a more or less deep groove 

 in the Dasyures and Thylacine. 



In the abdomen, the primary branches of 

 the aorta are sent off in the same order as in 

 most of the ordinary Mammalia, with the ex- 

 ception of the constant absence of an inferior 

 mesenteric artrry. This modification probably 

 relates to the simplicity of the mesenleric at- 

 tachment of the intestines above described. A 

 still more marked example of the oviparous 

 affinities of the Marsupialia, as exemplified in 

 the arterial system, occurs in the mode of 

 origin of the great arteries of the posterior 

 extremities. In Man and the ordinary Mam- 

 malia these are derived, as is well known, from 

 a single trunk on each side the common iliac 

 artery; in Birds from two primary branches of 

 the aorta, one corresponding with the external 

 iliac and femoral, the other with the internal 

 iliac and ischiadic arteries. In the Kangaroo 

 and Pbalangista vulpina the aorta gives off, 

 opposite the interspace of the two last lumbar 

 vertebra-, the iliac arteries ; but the^e are after- 

 wards resolved into the ordinary branches of the 

 external iliac of the placenta! Mammalia, with 

 the addition of the ilio-lumbar artery. The 

 trunk of the aorta, much diminished in size, 

 maintains its usual course for a very short 

 distance, and then gives off the two internal 

 iliacs, and is continued as the ' arteria sacra 

 media' to the tail. The transitional cha- 

 racter of this part of the marsupial sangui- 

 ferous system between the oviparous and pla- 

 cental types, is manifested in the large size of 

 the external iliacs as compared with the internal 

 iliacs, their greater share in the supply of blood 

 to the hinder extieinities, and the brevity of 

 the aortic trunk between their origins. In 

 most Birds the femoruls or external iliacs are 



smaller than the jschiadic or internal iliac 

 arteries subsequently given off. At the upper 

 part of the thigh the femoral artery divides into 

 two equal branches; the one which corresponds 

 with the radial artery in the fore leg (m, fig.\34) 

 principally supplies the foot in the Kangaroos ; 

 it passes along the back of the radius, between 

 the gastrocnemius internus and tibialis posticus, 

 and divides a little above the internal malleolus. 

 The smaller division (I, Jig. 134), which follows 

 the ordinary course of the femoral along the popli- 

 teal space, is lost upon the inner and posterior part 

 of the tarsus ; the larger branch winds over the 

 malleolus to the front of the tarsus, sends off 

 the anterior tarsal artery, and is then continued 

 along the inner and afterwards the under part of 

 the metatarsal bone of the long and strong toe. 



In /?g,134, a is the trunk of the coaliac artery ; 

 b 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 </, 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 Mammalia, and with 

 the femoral artery in Birds, (see Vol. i. p. 337, 

 jigs. 170, 23 ;) below these are given off A, 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; / the ex- 

 ternal, m 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 Chceropus, 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 

 cava, 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 ' 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 



