FROM TWELVE TO THIRTY-SIX SOMITES 179 
floor of the laryngotracheal groove directly continuous with the 
floor of the branchial portion of the pharynx at its hind end; the 
former bends up at about right angles to enter the narrow 
oesophagus (Figs. 87 and 88). 
Thus the whole pulmonary tract communicates widely with 
the pharynx at the 35s stage. Its complete delimination falls 
within the period covered by Chapter X. The continuity of 
the expansions that form the lung primordia, with the series of 
visceral pouches as shown in Fig. 100, is especially noteworthy 
as suggesting a theory of the phylogenetic derivation of the lungs. 
Fig. 103.— Reeconstructions of the liver diverticula of the chick. 
(After Hammar.) 
A.On the third day of incubation; from the left side; the divertic- 
ula arise from the anterior intestinal portal. 
B. Beginning of the fourth day; from the left side. 
a. i. p., Anterior intestinal portal. D. V., Indicates position of 
ductus venosus. g. b., Gall bladder. 1. d. d. (er.)., Dorsal or era- 
nial liver diverticulum. 1. d. v. (eaud.), Ventral or caudal liver 
diverticulum. pe. d., Dorsal pancreas. X., Marks the depression in 
the floor of the duodenum from which the common bile duct. is 
formed. 
Csophagus and Stomach. Immediately behind the pharynx, 
at the stage of 36s, the intestine narrows suddenly (primordium 
of cesophagus) and enters a small, spindle-shaped enlargement, 
the primordium of the stomach (Figs. 87, 88, 100). 
The liver arises in the chick as two diverticula of the entoderm 
of the anterior intestinal portal, one situated immediately above 
and the other below the posterior end of the ductus venosus, or 
fork of the omphalomesenteric veins (Fig. 103 A). This portion 
