SOCIETY OF THE UNIVERSITY OP ABERDEEN. f>5 



twins. The jejunum is 40 cm. in length and terminates quite natur- 

 ally in the ileo-crccal junction. The large intestine is perfectly regular 

 in both twins. 



With the exception of the foregoing points and the fact that the 

 gall-bladder was suppressed, the twins are normal and well formed, 

 and had it not been for the embryological error responsible for these 

 variations, there can be no doubt that two perfectly normal and 

 well-nourished twins would have resulted from the pregnancy. 



CASE II. As regards the second specimen a reference to Plates 

 XIII. and XIV. shows that the condition of fusion of the twins is very 

 similar to that in the first case, but is here more extensive. The fusion 

 involves not only the lateral abdominal walls but also the lateral thoracic 

 walls and two of the four upper limbs as far as the wrist. It will be 

 unnecessary to pursue the successive stages of the dissection in this 

 instance, as they were identical with those of the first case. Precisely 

 the same variations were found in connection with the alimentary 

 canal and liver, the only alteration being that there was a gall-bladder 

 in the second case and none in the first. 



The heart and great vessels, as is only to be expected from the 

 thoracic fusion, present, however, some remarkable and interesting 

 variations (See Fig. 1). To take the great vessels first, there is, in 

 the case of the right twin, a right-sided aorta and a pulmonary trunk 

 both of which arise from the same ventricle. The aorta gives off a 

 large branch which communicates with the left pulmonary artery by 

 means of a patent ductus arteriosus, and then breaks up in an axis- 

 like manner into a left subclavian, a left common carotid and a right 

 common carotid. The arch of the aorta thereafter gives off the right 

 subclavian artery as a separate trunk. 



In the case of the left twin there is a left-sided aorta and a pul- 

 monary trunk. The aorta gives off in the first instance a single trunk 

 which divides into the right and left common carotid arteries. Im- 

 mediately beyond the origin of this carotid trunk the arch gives off 

 the right subclavian, and beyond that again the left subclavian. 

 Having given off these three branches the aorta communicates with 



