114 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



limb buds is the milk line, a thickened ridge of ectoderm which forms the anlages 

 of the mammary glands. The tail is long and tapering. Between its base and the 

 umbilical cord is the genital eminence (Fig. 120). 



Human embryos of this stage or slightly older vary considerably in size 

 (Fig. 119). They differ from pig embryos in the greater size of the head, the 



Metencephalon N. Irochlearis 



M I SI iiccphiilon 



olontis 



Cling. 

 Gang, jiignlih 

 Gang, prirosii 



Gang. Fror 

 Gang, nodos. ii. l 



N. accessiini 



N. hypogliissii 



Atrium 



Lu}ig 



Gang. cn-v. S 



Septum transvcnum 

 Lircr 



Mesonepliro^ 

 . thora 



mbilical lOrd 



Fig. 120. — Lateral dissection of a 10 mm. pig embryo, showing the viscera and nervous system from 

 the right side. The eye has been removed and the otic vesicle is represented by a broken Une. The 

 ventral roots of the spinal nerves are not indicated. X 10.5. n., Nerve; r., ramus. 



shorter tail, the much smaller mesonephric region, the longer umbilical cord, and 

 the less prominent segments. The yolk sac is pear-shaped and the yolk stalk is 

 long and slender. 



Central Nervous System and Viscera.— Dissections show well the form and 

 relations of the organs (Figs. 120, 121 and 122). Directions for preparing dis- 

 sections are given in Chapter VI. 



