32 LABORATORY OUTLINES FOR EMBRYOLOGY 



rior to the lung-buds the gut narrows into the short 

 oesophagus. Soon it enlarges somewhat to form the 

 stomach. The ventral evagination of the duodenum is 

 the liver. In the hind-gut the ventral bladder-like 

 evagination, as was mentioned before, is the allantois. 



From your study of these sections, reconstruct the ali- 

 mentary tract and its appendages and make a drawing of 

 it as an opaque object, lateral view. 



THE PIG EMBRYO 



I. Ten-millimeter Embryo 

 a. Whole Embryo 



Remove all the membranes from a ten-millimeter pig 

 embryo. Examine the external form with the dissecting 

 microscope or the hand lens. It will be noticed that the 

 head is very large in comparison with the body. It 

 forms nearly a right angle with the remainder of the body. 

 This marks the location of the hind-brain. Anterior to 

 the hind-brain is an enlarged part which makes a rounded 

 angle. This marks the position of the mid-brain. The 

 fore-brain is now composed of two rounded lobes, the 

 rudiments of the cerebral hemispheres. In the angle 

 ventral to the fore-brain and the mid-brain is the lens 

 of the eye surrounded by the edges of the optic cup. 

 Extending from the eye ventrally is a depression or 

 groove, the lachrymal groove. The lachrymal groove 

 leads to an invagination forming a cup-like pit ventral 

 to the anterior part of the fore-brain. This invagination 



