94 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



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 mesen- 

 cephalon. Ventro-lateral to the metencephalon and myelencephalon occur 



Gang, super ius K . 9 Otocyst 



Gang, acousticum n. 8 

 Gang, geniculi n. 7 



Gang, semilunare n. 5 



Metencephalon 



Gang, jugulare n. 10 

 Gang, nodosum n. 10 



N. accessories 



Gang. Froriep 

 Gang. ceru. I 

 N. hypoglossus 

 Cervical sinus 



Small intestine 



Mesencephalon 

 N. oculomotorius 



Diencephalon 



ng. petrosum 

 cj 



Lens opening 

 Olfactory pit 

 Telencephalon 

 Yolk sac 

 Allantois 



Ventricle 

 AUantoic stalk 



Hind-gut 



FIG. 95. Dissection of a 5.5 mm. pig embryo, showing the nervous system and viscera from the 



right side. X 18. 



in order: the 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 ganglia. 

 They are in order the superior, or root ganglion of the glossopharyngeal 

 nerve with its distal petrosal ganglion; the ganglion jugulare and distal 



