192 



STUDY OF PIG EMBRYOS. 



original connection with the pharynx has been lost. The anlage is now isolated 

 from its parent germ-layer and is imbedded in mesenchyma. It is solid, for 



Fig. 118. — Pig, 12.0 mm. Transverse Series 5, Section 321. 

 ././, Fourth aortic arch. Art.v, Vertebral artery, .lit. External auditory cleft, cl.iii, Third internal gill 

 cleft. C »«/, Ganglion nodosum. //■,•, Hyokl arch. Jug, Jugular vein. L. V, Lateral ventricle. -\',<, 

 Nasal pit. N.ctrv.i, First cervical nerve. N.ceru.z, Second cervical nerve. X. //, Spinal accessory 

 nerve. JV./g, Hypoglossal nerve. Nv.2, Main trunk of second cervical nerve. OI.pl, Olfactory plate. 

 A'.ex.q, Ramus externus of the glossopharyngeal. Sp.c, Spinal cord. Thru, Thymus. Thyr, Thyroid. 

 Tr, Trachea. ■ 22 diams. 



the cavities of the thyroid follicles are not developed until considerably later. 

 Just above the third gill cleft may be seen a large, darkly stained mass, 



