THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



At the cervical bend the head is flexed at right angles with the body, 

 bringing the ventral surface of the head close to that of the trunk, and 



Branchial groove 1 

 Hyoid arch 



Cervical flexure 

 Branchial arch j 



Cervical sinus 



Upper limb 



Milk line 



Mesodermal segmen 



Myelencephalon 



^/Cephalic flexure 



^Eye 



Maxillary process 

 Mandibular process 

 Olfactory pit 



Yolk sac 



Umbilical cord 



Lower limb b 

 FIG. 118. Exterior of a 10 mm. pig embryo, viewed from the right side. X 7. 



it is probably owing to this flexure that the third and fourth branchial 

 arches buckle inward to form the cervical sinus. Dorsad, the trunk forms 



Cervical flexur 



Maxillary process 

 Attachment of amnion 



External ear 

 Mandibular 



Upper limb bud 

 Mesodermal segment 



Lower limb bud 



FIG. 119. Exterior of a human embryo of 12 mm. viewed from the right side, showing attach- 

 ment of amnion (cut away) and yolk stalk and sac. X 4. 



a long curve more marked opposite the posterior extremities. The 

 reduction in the trunk flexures is due to the increased size of the heart, 

 liver, and mesonephroi. These organs may be seen through the translu- 



