PAPERS OX BIOLOGY AND AGRICULTURE 117 



other; and because of their relations to the two post 

 cavae, it would appear that the larger heart, the more 

 ventral one, is of the smaller pig, while the slightly smal- 

 ler one is likewise of the larger pig. 



Just anterior to the larger heart the main dorsal aorta, 

 coursing from its right ventricle, bifurcates to form the 

 two aortae, each of which passes to a normal position in 

 its respective animal. That aorta supplying the larger 

 animal is joined at once by a secondary aortic arch com- 

 ing from the right ventricle of the smaller heart ; so that 

 the two hearts thus have a common bond in these con- 

 nections to the aortae. Posteriorly each aorta gives rise 

 to the normal intercostals, eoeliac and mesenteric arter- 

 ies; although in the smaller animal these branches are 

 greatly reduced and largely devoid of blood content, and 

 thus were relatively difficult to trace. Renals, iliacs and 

 umbilical arteries are present in the larger animal, but no 

 umlulicals were recognized in the smaller. Furthermore, 

 a variation is to be noted in the point of attachment of 

 the umbilicals to the aorta ; instead of attaching to the 

 internal iliac as we would expect, here the umbilicals con- 

 nect with the aorta considerably anterior to the iliacs. 



The carotid arteries have not retained their identity 

 of relationship to each animal; but all are united to the 

 common aorta (Fig. 3). A single brachiocephalic artery 

 arises from the arch of the smaller aorta and divides in- 

 to two carotids, from which later arise a corresponding 

 subclavian artery, distributed to the respective limb. 

 From the bend of the aorta, just in front of the larger 

 heart, a pair of arteries continue forward into the head 

 region and form the paired carotids and the left subcla- 

 vian of the larger animal : while the right subclavian of 

 the larger animal arises independently from the aortic 

 arch of the smaller heart (Fiu\ 3). The complete dis- 

 tribution of these arteries into the head region was not 

 ascertained, as the absence of the blood content made 

 their identification extremely difficult ; and accordingly 

 no knowledge is available of the relation of the paired 

 internal carotids to the circle of Willis, so graphically 

 figured by Carey in his description of this region in his 

 monster. 



