DEVELOPMENT OF THE ELASMOBRANCH LIVER 337 



the anterior intestinal portal and the sinus venosus as a single 

 median ventral pouch from which the lateral pouches secondarily 

 arise, and second, the recognition of the fact that the medita 

 pouch which can be distinguished when the liver reaches the rin- 

 lobed stage consists of two portions, named in accordance with 

 the nomenclature suggested by Goeppert ('93) the 'pars hepatica' 

 which lies anteriorly and joins with the two lateral pouches in 

 forming the true hepatic parenchyma, and a posterior portion 

 called the 'pars cystica' which forms the gall bladder and the 

 cystic and common bile ducts. Brachet followed the history of 

 the latter structures in detail, but gives little information as 

 to the history of the hepatic ducts, although he recognized that 

 they were formed from the bodies of the lateral pouches and con- 

 sidered that these pouches were reduced in caliber in the course of 

 their transformations. In the Ergebnisse for the same year 

 Brachet ('97) repeats his conclusions and summarizes the preced- 

 ing literature since the time of Balfour. 



Rilckert's work ('96) on the development of the spiral val\^e in 

 Pristiurus is illustrated by three reconstructions, two of which 

 include the gall bladder and ductus choledochus and illustrate 

 well the forward migration of the former structure. Riickert 

 describes the migration of the ostium of the ductus choledochus 

 in relation to the vitelline duct and its movement from left to 

 right along with the spiral valve in later stages. 



Mayr ('97) in his account of the development of the pancreas 

 in Pristiturus and Torpedo incidentally describes the condition 

 of the liver in several embryos. His description coincides with 

 that of Balfour and Brachet, but he emphasizes the fact that in 

 early stages the pars hepatica is single anteriorly and that the 

 two lateral pouches diverge from the median line as they extend 

 backward. 



Choronschitzky ('00) published a paper of some magnitude, 

 describing the development of the liver and certain other viscera 

 in all classes of vertebrates. Torpedo was employed as a repre- 

 sentative of the fishes. He gave an account of four stages of this 

 form, the youngest being one in which the liver consisted of a 

 median and two lateral pouches from which four 'secondary' 



