IOO 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



cervical sinus (see Fig. 88). The brain is differentiated into the five regions, 

 telencephalon, dicnccphalon, ■mesencephalon, metencephalon and myelencephalon. 

 The spinal cord is cylindrical and gradually tapers off to the tail. The anlages 

 of the cerebral and spinal ganglia and the main nerve trunks are shown. The 

 oculomotor nerve begins to appear from the ventral wall of the mesencephalon. 

 Ventrodateral to the metencephalon and myelencephalon occur in order the 



Sup. gang. n. p Otocyst 



Acustic ganglion 



Jugular gang. u. 10 

 Gang, nodosum n. 10 

 N. accessorius 



Ca 

 Gang. cert). 

 N. hypoglossus 



Cervical sinus 



Atrium 



Ventral lobe liver 

 Dorsal lobe liver 



Thoracic gang. I 

 Mcsonephros 



Small intestine 



Geniculate gang. n. 7 



Semilunar gang. n. 5 



Metencephalon 



Mesencephalon 

 ■N. oculomotorius 



Dicnccphalon 



Petrosal gang, 

 n. Q 



Lens opening 

 Olfactory pit 

 Telencephalon 

 Yolk-sac 

 Allantois 



Ventricle 



Allantoic stalk 

 Hind-gut 



Fig. 90. — Dissection of a 5.5 mm. pig embryo, showing the nervous system and viscera from the right 



side. X 18. 



semilunar ganglion and three branches of the trigeminal nerve, the geniculate 

 ganglion and nerve trunk of the n. facialis, the ganglionic anlage of the n. acusticus 

 and the otocyst. It will be observed that the nerve trunks are arranged with 

 reference to the branchial arches and clefts. Caudal to the otocyst a continuous 

 chain of cells extends lateral to the neural tube into the tail region. Cellular 

 enlargements along this neural crest represent developing cerebral and spinal 



