454 Mabel Bishop 



path between the overlapping rami and emerges at its most dorsal part, 

 only to turn abruptly at a sharp angle and disappear into the interior of 

 the cranium between the projecting rami and the protruding shelf of 

 bone above them. Again the value of the specimen for future study 

 opposed further investigation and I did not open the cranium to follow 

 the course of this artery. Yet I thinly no serious check has been placed 

 upon its identification, for from the data at hand I feel that it may be 

 safely interpreted as a Median Compound Internal Maxillaet. Al- 

 though the median eyeball had been removed with no special reference 

 to the preservation of underlying parts, there are still present within the 

 orbit traces of nerve fibers and other tissue. On the anterior surface of 

 the orbit, on either side of the median axis, and close to the roof of the 

 cranium are two minute foramina. Issuing from them are two black 

 threads, so to speak, which I mistook at first for discolored nerve fibers, 

 but which upon closer examination proved to be injected blood vessels. 

 It takes but a slight stretch of the imagination to suppose them branches 

 of an internal maxillary, which normally divides within the eye-orbit, and 

 such a vessel is the one in question. If this be granted, it is not diffi- 

 cult to trace back to their parent artery the intercranial course of the 

 infraorbitals, whose external ramifications have already been followed, 

 and whose origin is known to be from an internal maxillary. These two 

 suppositions seem to me to render valid the identification of the artery 

 under discussion as a Median Compound Internal Maxillary. The 

 hypothetical relations are indicated in the plate by dotted lines. 



It remains to be demonstrated how the changes in the mid-region have 

 come about, and their significance. In this cosmobiotic series of organ- 

 isms leading through dicephali and ischiopagy to duplicate twins, Teras 

 XII represents one of the earliest stages. This specimen is developed 

 but a little beyond normal and the doubling ceases externally at about 

 the level of the angle of the mouths. Naturally the blood vessels of 

 this region, as well as the other parts, exhibit the doubling also. As 

 a cosmobiotic head passes beyond a single individual in development it 

 grows further and further away from that single stage, but nearer and 

 nearer to two separate and distinct heads. It should be borne in mind 

 that I do not mean that these progressive changes take place in a single 

 individual. Each represents but one stage in the series, individual links 

 in a chain, which may be made up of an infinite number of links of 

 which the last two represent duplicate twins. 



Since the arterial system supplies all parts of an organism, it forms 

 by its distribution an outline of the entire anatomy of the individual,. 



