SOCIETY OP THE UNIVERSITY OF ABERDEEN. 71 



in his views upon this point. The hypothesis upon which the lateral 

 fusion was explained suffices, therefore, for the single duodenal and 

 jejunal tubes as well as for the single liver. 



3. The Suppression of the Gall-bladder in the one ruse mid it.** /'y v.svwr 

 in tin' other. As the gall-bladder is known to be developed normally 

 as a diverticulum from the common hepatic stalk in the second month, 

 it is perfectly easy to understand the suppression of this viscus in the 

 one case and its presence in the other ; it is at the same time impos- 

 sible to offer any theory as to why the gall-bladder diverticulum should 

 thus grow out in the one case and not in the other. 



4. The, Partial Fuxioti of the Heart and the Peculiar Condition of the 

 Auricle* and Ventricles. From the description which has already been 

 given of the apparently single heart it will be sufficiently obvious that 

 it is in reality a question of the partial fusion of two originally dis- 

 tinct tubular hearts. As the inferior vena; cava; unite to form a single 

 structure just before their termination in the functional right auricle, 

 and as there are but two auricles with four auricular appendages, it 

 seems fairly certain that the two originally distinct tubular hearts 

 have fused together in the region of the sinus venosus (see Fig. 4). 

 This is further borne out by the condition of the ventricles. On this 

 assumption it is not very difficult to understand what has taken place. 



Under normal conditions the sinus venosus shifts towards the 

 right side of the primitive auricle, and so eventually opens into that 

 part of it which becomes the right auricle of the adult heart, forming 

 its atrium and the coronary sinus. The primitive auricle sends out 

 an appendix on each side which grows forwards around the bulbus 

 arteriosus, whilst the primitive auricle itself becomes differentiated 

 into a right and a left chamber by the growth of two septa the 

 septum primum and the septum secundum the foramen ovale being- 

 nothing more than the interval left between these two auricular septa. 

 In this particular instance the sinus venosi of the two twins have 

 fused together to form a common cavity (Fig. 4), but this fusion has 

 not affected, or perhaps only very slightly, the primitive auricles, as 

 is evidenced by the presence of the four auricular appendages. The 



