ARTERIES OF MAMMALIA. 539 



the marsupial artery, d, which is similarly resolved : most of the 

 branches coursing to the back part of the marsupial bones and 

 bending upward or forward upon the abdominal muscles attached 

 thereto, in a course analogous to that of the so-called ( epigastric ' 

 artery in Man. The iliac trunk, b, is then continued a short way, 

 and resolves itself into the short trunks of three plexuses : the 

 outermost, e, take a course obliquely to the outer side of the 

 thigh, analogous to that of the ' external circumflex ' branch of 

 the femoral in Man, the middle division representing the femoral 

 trunk has a course of three lines before its resolution into the 

 ' femoral plexus,' f, which continues the usual course to the ham : 

 the third short trunk, representing the ' internal iliac,' g, resolves 

 itself into a plexus distributed to the parts supplied, in Man, by 

 the sciatic, gluteal, and pudic arteries ; but one branch is con- 

 tinued superficially down the back part of the hind leg, t, to the 

 tarsal bone supporting, in the male, the spur : it accompanies the 

 duct of the spur-gland in the lower half of its course. The ar- 

 terial system in Echidna is similarly characterised by the subdi- 

 vided plexiform disposition of many of the artei'ies. The caudal 

 artery, ib. A, pursues a wavy course beneath the broad caudal 

 vertebra, in Ornitliorhynchus. In Marsupialia, after the coro- 

 nary arteries, the primary branches from the arch of the aorta rise 

 in some species by three, in others by two trunks. The broad- 

 chested Marsupials, the Koala and Wombat, for instance, are 

 those in which the left carotid, g', fig. 402, and subclavian, h\ 

 arise separately from the arch; the arteria innominata dividing 

 into the right subclavian and carotid, ib. g, A, as in Man. In 

 most Marsupials the innominata gives off both carotids, g, g, fig. 

 401, as well as the right subclavian, h. The common carotid in 

 the Kangaroo gives off the thyroid artery, and divides opposite 

 the transverse process of the atlas into the ecto- and ento-carotids. 

 The latter describes a sharp curve at its origin, passes along 

 the groove between the occipital condyle and the paroccipital to 

 the basisphenoid which it pierces. The vertebral arteries are 

 given off by the subclavians, and pass to the skull, as usual, 

 through the cervical vert ebr arterial foramina. They unite be- 

 neath the medulla oblongata to form the basilar artery, which 

 sends off 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 smaller ento- 

 carotids to form the circle of Willis. The brachial artery divides 

 early into ulnar and radial branches : in the Koala, Wombat, 



