IO2 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



hyoid arch is a triangular rounded elevation, the tuberculum impar, which later 

 forms a part of the tongue. At an earlier stage the median thyreoid anlage grows 

 out from the mid-ventral wall of the pharynx just caudal to the tuberculum 

 impar. The ventral ends of the second arch fuse in the mid-ventral line and 

 form a prominence, the copula. This connects the tuberculum impar with a 



Pharynx 



Metamere 4 Rathke's pocket 



Interatrial 



foramen 



Lung bud 



Hepatic 

 diverticulum 



Ventral 

 pancreas 



Cranial limb 

 intestine 



Genital ridge 



Isthmus 



Mesencepkalon 

 Diencephalon 



Bulbus cordis 

 Telencephalon 

 Ventricle 



Septum trans- 

 versum 



Liver 



Yolk-sac 



Allantois 



Tail-gut 



Cloaca 



Metanephros 



Spinal cord / J Caudal limb of intestine 



Mesonephros Mesonephric duct 



FIG. 91. Median sagittal dissection of a pig embryo of 6 mm., to show viscera and neural tube. X 18. 



rounded tubercle derived from the third and fourth pairs of arches, the anlage 

 of the epiglottis. Its cephalic portion forms the root of the tongue (compare 

 Fig. 151 A and B). Caudal to the epiglottis are the arytenoid ridges and a slit 

 between them, the glottis, leads into the trachea. 



The branchial arches converge caudad and the pharynx narrows rapidly 

 before it is differentiated into the trachea and esophagus (Figs. 99 and 100). 

 Laterally and ventrally between the arches are the four paired outpocketings of 



