294 



STUDY OF PIG EMBRYOS. 



which extend farther laterally the first and second entodermal gill-pouches. In 

 the figure can be seen a small depression extending downward from the cesophageal 

 or posterior end of the pharynx. This depression marks the beginning of the second 

 cleft. Nothing is seen of the third and fourth clefts in this section, as they both 

 lie nearer the median plane. The pocket or diverticulum of the cervical sinus, 



Jug.'" G.jug. 



Ph. 



Ac.F. 



R.L. 



EC. 



G.petr. 



G.nod. 



Cerv.S. 



N.12. 



Cerv.f). 



Jug."" 



FIG. 202. PIG, 12.0 MM. No. 7. SAGITTAL SECTION 25. 



Ac.F, Acustico-facial ganglion complex. Aur, Auricle of the heart. Cerv.S, Diverticulum of the cervical sinus* 

 just in front of which shows the anlage of the thymus, which is deeply stained. Cerv. 6, Sixth cervical nerve- 

 Cce, Ccelom around the heart or pericardial cavity. EC, Ectoderm. G.jug, Ganglion jugulare of the vagus 

 nerve. G.nod, Ganglion nodosum of the vagus nerve. G.petr, -Ganglion petrosum of the glosso-pharyngeal 

 nerve. G.tri', Ganglion of the trigeminus nerve. H, Lateral wall of the cerebral hemisphere. Jug' -Jug'"' , 

 Jugular vein (Jug', Behind the trigeminus. Jug" , Branch in front of the trigeminus. Jug'" , Main stem 

 behind the vagus. Jug"", Main stem descending to join the duct of Cuvier). m, An undetermined 

 structure, probably the anlage of a lingual muscle. Md, Mandible. JV-5, Root of the fifth or trigeminal nerve. 

 N.op, Optic nerve. N. 12, Twelfth or hypcglossal nerve. Ot, Otocyst. PA. Pharynx. R.L, Recessus lateralis 

 of the fourth ventricle. Ve, Small branch of the jugular vein. Vent, Ventricle of the heart. X 22 diams. 



Cerv.S, lies near the ganglion nodosum, G.nod. From its appearance it might easily 

 be mistaken for the section of a gill-cleft, but it is in reality lined not by entoderm 

 but by ectoderm, and its cavity can be easily traced through the series of sections 

 of the exterior of the embryo where the epithelium lining the sinus becomes con- 

 tinuous with the epidermis. Cfephalad from the sinus, but close to it, lies a small 



