n6 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



cent body wall, and the position of the septum transversum may be noted 

 between the heart and the liver, as in Fig. 120. The limb buds are larger 

 and the umbilical cord is prominent ventrad. Dorsally, 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 



N. ocidomotorius 



Metencephalon N. trochlearis 

 Gang. n. 5 \ I Mesencephalon 

 Gang. nn. 7 and 8 \ 



N. facialis 

 Gang, si perius n. 9 

 ^' Gang, jugular e n. 10 

 Ga.ig. petrosum n. 9 



Gang. Froriep 

 Gang.nodosum n. 10 



N. accessorius 



iencephalon 



phthalmic r. n. 5 



N. opticus 



Maxillary r. n. 5 

 Telencephalon 



Mandibular r. n. 5 

 Chorda tympani n, 7 



Ventricle 



Mesonephros 



Gang, thorac. 10 



Umbilical cord 



Genital eminence 



FIG. 1 20. 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 line. The ventral roots of the spinal nerves are not indicated. X 10.5. n., Xerve; 

 r., ramus. 



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 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. 



