THE MCLLERIAN DUCT. 123 



duct (fig. 149). To this duct it presently adheres intimately, and then continues 



Fig. 147. FOUR SECTIONS THROUGH THE ANTERIOR PART OP THE 



SEGMENTAL DUCT OF A SCYLLIUM EMBRYO. (Balfour.) 



The figr.re shows how the segmental duct becomes split into the 

 Wolffian duct dorsally and the Miillerian duct or oviduct ventrally ; 

 Wd, Wolffian duct ; od, Miillerian duct or oviduct ; sd (in D), 

 segmental duct. 



to grow backwaras for a certain distance as a thicken- 

 ing of the epithelium of that tube, the thickening 

 becoming gradually separated off from before back- 

 wards, and the lumen passing along it. Further back 

 it ceases to grow thus in connection with the Wolffian 

 duct, but is prolonged as an independent cellular cord, 

 which lies in a groove along the side of the Wolffian 

 duct (Balfour and Sedgwick). 



Entering the genital cord, 1 the two Miillerian ducts 

 lie at first on the mesial side of the corresponding 

 Wolffian ducts, but lower down pass behind them ; 

 they finally come again between these ducts, lying 

 close together, and, according to Mihalkovics, approach 

 close to the sinus urogenitalis, which by this time is 

 formed out of the ventral part of the cloaca (see p. 128) 



without actually opening into it for some time. The Miillerian ducts fuse together 

 below into a single tube (fourth month) ; the fusion begins not at the lower end, 



Fig. 148. SECTIONS FROM THE CHICK SHOWING TWO OF THE PERITONEAL INVAGINATIONS WHICH GIVE 



RISE TO THE ANTERIOR PART OF THE MtfLLERIAN DUCT. (Balfour and Sedgwick. ) 



<jrr 2 , second invagination ; gi" 3 , third invagination ; r 2 , epithelial ridge between them ; Wd, 

 Wolffian duct. These structures form the pronephros of Balfour and Sedgwick (see note, p. 115). 



Fig. 149. Two SECTIONS FROM THE CHICK 



SHOWING THE JUNCTION OF THE TER- 

 MINAL SOLID PORTION OF THE MlJL- 

 LERIAN DUCT WITH THE WOLFFIAN 



DUCT. (Balfour and Sedgwick.) 



In A, the terminal portion of the duct 

 is quite distinct ; in B it has united 

 with the wall of the Wolffian duct, md, 

 Miillerian duct ; Wd, Wolffian duct. 



but a short distance away from 

 this (fig. 150, 3), and proceeds 

 both downwards towards the 

 future orifice and upwards for a 



1 A name given to the thickened mass of tissue which surrounds the Wolffian ducts as they course 

 together to the cloaca behind the stalk of the allantois (afterwards the base of the bladder). 



