Arteries in Monsters of the Dicephalus Group 459 



treniity divides into the anterior and posterior aortas. The anterior 

 aorta is likewise short and terminates in the left subclavian and a cepha- 

 lic, which in turn bifurcates into right and left common carotids to 

 supply Head B. The right subclavian, instead of arising from the 

 anterior aorta at the origin of the left, has retained a dorsal origin, and 

 arises from the dorso-lateral (right) wall of the posterior aorta at the 

 extremity of the aortic arch. It crosses the dorsal surface of the trachea 

 and oesophagus diagonally and to the right and arrives at a position 

 opposite the origin of the left subclavian. It then arches over the first 

 rib on the right side of the body and continues its course to the right 

 forelimb in normal manner. 



Head A is not supplied by any portion of the arterial system thus far 

 described, but has an independent supply direct from the heart. Parallel 

 to and close beside the aortic trunk there arises from the left ventricle 

 another artery of lesser diameter (8 mm.), which is continued anteriorly 

 and to the right of the trachea to a point a little posterior to the origin 

 of the conmion carotids destined to supply head B. Here this new 

 vessel also bifurcates into right and left common carotids to supply 

 Head A. Upon making a longitiidinal section of the heart a few milli- 

 meters to the normal right of the median axis, a small cavity was opened 

 up which is in communication with the left ventricle by means of a semi- 

 lunar valve. During normal development the semi-lunar valve marks 

 the division between ventricle and aortic bulb, and thus the new cavity 

 is shown to be a new bulbus arteriosus. Therefore the vessel arising 

 from it is a second aorta, and since it is continuous with the cephalic 

 trunk, it may be termed an aorto-cephalic trunk. It gives off no branches, 

 since all that are needed are given off by the systemic aorta which sup- 

 plies component B, but terminates in a right and left common carotid 

 destined to supply head A. Just above the semi-lunar valve but poste- 

 rior to the root of the aorta-cephalic trunk, there arises from the bulbus 

 a small, short artery which crosses over to the other aortic trunk on the 

 posterior side, and unites with it about 7 mm. from its root. This branch 

 is probably the remnant of a primitive arterial arch, as will be shown 

 presently. 



The independent arterial supply to head A is of great importance to 

 the cosmobiotic theory. After following the course of the arteries in the 

 two heads, I shall offer hypothetical explanations of the conditions found 

 in the roots of the great blood vessels, and point out their significance. 



Since there are present in Teras XV two completely separated heads, 

 each with its normal parts, the heart is called upon to furnish a double 



