Arteries in Monsters of the Dicephalus Group 447 



during the short life of this cosmobion, since the stomach was filled 

 with curds. The appearance of the mouth cavity, together with the fact 

 that the axis of head B makes almost a straight angle with the body 

 axis, indicates strongly that this was probably the suckling head. Head 

 A is turned at a somewhat broader angle from the median axis of the 

 monster, and the snout is directed more ventrally than that of the other 

 component, thus forming a more acute angle between head and chest 

 [see Plate III]. If the mode of suckling in ruminants be recalled, 

 it will be readily seen how very difficult it would be for this head (A) 

 to suckle, since it would necessitate an awkward twisting and distortion 

 of the whole dicephalous region. It seems only logical, therefore, to 

 conclude that the head most nearly normal in position would usurp 

 the feeding function from the beginning and be constantly favored at 

 the expense of position of the other head, so that, although at the present 

 stage the difference in position of the two components is not extremely 

 great, it is quite possible to foresee that if the animal had lived longer, 

 head A would have come to be thrust even further from the normal and 

 to assume an almost parasitic position.® There is still another reason 

 to support my conclusion, which I shall point out when speaking of 

 the blood supply in the head region. 



An approximate idea of the stage of doubling of Teras XV may be 

 gained by comparing it with Forster's human diprosopus tetrotus [Tafel 

 I, Fig. 7] and with Hirst and Piersol's [page 149, Fig. 77]. The two 

 heads of Teras XV are united in the occipital region, the rmion involv- 

 ing the bones, thus resulting in a composite occipital. The ears on 

 the inner lateral sides are separate, though the ear of head B is crowded 

 a little above that of the other component. Behind them the heads 

 appear at first sight to be superficially united, but closer examination 

 shows that a union does not really exist, since hair is found growing 

 between and behind the ears down to the composite occipital region. 

 Both outer ears and all four eyes are normal. The brains of this 

 dicephalus have been removed and preserved. These are also normal 

 yer se and conjoined only in the region of the medulla oblongata just 



^This explains the case told me by Professor Wilder, which he recalls from 

 memory, of an adult double-headed ox widely exhibited about twenty years 

 ago, in which one head, although of practically the same size as the other, 

 did not function In alimentation, but was borne habitually upon the side of 

 the other head, which was held so as to continue the main axis of the body. 

 In this monster the functional head was also the left. 



