PROCEEDINGS OF SECTION D. 509 



The Alimentary System. — Each twin possesses a stomacli fully 

 formed and developed and composed of four parts — a rumen, a reticulum, 

 a psalterium, and an abomasum. From the abomasum proceeds a 

 duodenum, which unites with the duodenum of the opposite twin, so 

 that there is a single duodenal tube common to both twins. The 

 duodenal tube measures in all 20cm. — 11cm. belonging to the right 

 twin and 9cm. to the left twin. From the junction of these two duodena 

 proceeds a single jejunum, common to both twins, and measuring 162cm. 

 The jejunum possesses a mesentery on both sides, with blood vessels 

 running along both borders, and terminates belov/ in a slight pouch- 

 like dilatation 3cm. in diameter. From this point onwards each twin 

 possesses its own independent alimentary canal ; consequently, arising 

 from the pouch-like dilatation in which the common jejunum ends, are 

 the two ilea — one for each twin, and each of which measures 67cm. Each 

 ileum terminates at its own ileo-caecal junction, the position of which 

 is marked by a large lymph gland. The large intestine is perfectly 

 normal in each twin, and measures 74cm. in length, whilst the ceecal 

 portion is 6cm. in length. 



The alimentary canal is, therefore, perfectly normal, with the 

 exceptions of the fused duodena and of the single jejunum common to 

 both twins — that is to say, the alimentary abnormalities are exactly 

 as they were in the two human instances previously referred to. 



The liver is a single structure common to both twins, which sits, 

 as it were, astride of the common and single duodenal tube. That the 

 single liver is the result of the fusion of two separate livers seems almost 

 certain, because two gall bladders are present, and there are two distinct 

 series of biliary ducts. 



The pancreas is duplicated — that is, there is one for each twin. 

 It is normal in position in each case, being applied to the stomach and 

 duodenal tube. The common bile duct and the duct of Wirsung join 

 together on each side to form a single duct, and the single ducts so 

 formed — one in each twin — unite together and open by a common 

 orifice into the duodenal tube exactly opposite the commencement of 

 the jejunum. 



The Respiratory System. — The respiratory system is perfectly 

 norm^al. Each twin possesses two pleural membranes and two lungs. 



The Vascular System. — The vascular system, as might be expected 

 from the thoracic fusion, is extremely abnormal. There is a single 

 pericardial cavity, mesially situated, containing a single heart common 

 to both twins. 



The Heart : External Configuration. — The heart is, as stated, a 

 single structure common to both twins. It lies mesially, in the peri- 

 cardial sac. What appears externally to be a large left ventricle 

 occupies the major part of the anterior surface, and forms the true 

 cardiac apex. This ventricle is separated from what appears to be a 

 right ventricle by an interventricular groove. At the basal portions 

 of these apparent ventricles, and overlapping them, is what appears to 

 be a single auricle ; but there are, nevertheless, four distinct auricular 

 appendages. 



