THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



121 



the posterior extremities. The reduction in the trunk flexures is due to the in- 

 creased size of the heart, liver and mesonephroi. These organs may be seen 



Myelencephalon 



Br. cleft I 

 II void arch 



Cervical flexure 

 fir. arch III 



Cervical sinus 



Upper 



limb bud 



Milk line 



Mes. segment 



Cephalic flexure 

 Eye 



Maxillary process 



Mandibular 

 process 

 Olfactory pit 



Yolk-sac 



Umbilical cord 



Lower limb bud 



Fig. 113. — Exterior of a 10 mm. pig embryo viewed from the right side. X 7- Br. arch III, branchial 

 arch three; Br. cleft I, first branchial cleft; mes. segment, mesodermal segment. 



Cervical 



flexure 



through the translucent body wall and the position of the septum transversum 

 may be noted between the heart and the diaphragm, as in Fig. 115. The limb 

 buds are larger and the umbilical 

 cord is prominent ventrad. Dor- 

 sally the mesodermal segments may 

 be seen and extending in a curve 

 between the bases of the limb buds 

 is the milk line, a thickened ridge 

 of ectoderm which forms the an- 

 lages of the mammary glands. The 

 tail is long and tapering. Between 

 its base and the umbilical cord is 

 the genital eminence (Fig. 115). 



Human embryos of this stage 

 or slightly older, vary considerably 



/t-,. \ rpi j-rr c Fig. 114. — Exterior of a human embryo of 12 



in size (Fig. 114). They differ from , . . 



b ^' J mm., viewed from the right side, showing attachment 



pig embryos in the greater size of of amnion (cut away) and yolk-stalk and -sac. X 5- 



Yolk-sac 



