CKANIAL SYMPATHETIC GANGLIA IN THE PIG 87 



ganglion. As indicated above and illustrated in figure 3, cells 

 of medullary origin wander out from the mantle layer in the wall 

 of the rhombencephalon into the motor root of the trigeminal 

 nerve and advance peripherally along its fibers. The cells of 

 nervous origin accompanying the fibers of the mandibular nerve 

 are, therefore, derived from two sources, viz., the rhombencepha- 

 lon and the semilunar ganglion. 



In parasagittal sections of embryos of the pig 12 to 15 mm. 

 in length which pass close to the median surface of the proximal 

 part of the mandibular nerve, small groups of cells may be ob- 

 served which are removed by only a short -interval from the 

 periphery of the semilunar ganglion and are closely associated 

 with the growing fibers of the mandibular nerve. These cell- 

 groups constitute the anlage of the otic ganglion. In similar 

 sections of embryos 17 mm. in length, as illustrated in figure 11, 

 Ot, these aggregates of cells have become larger and are some- 

 what farther removed from the periphery of the semilunar gan- 

 glion. The ganglionic anlage now appears as an irregular mass 

 of cells which is closely associated with the median surface of 

 the mandibular nerve. In embryos 21 mm. in length, the anlage 

 of the otic ganglion has increased materially in size and the 

 major portion of it lies distinctly below the path of the nerve 

 and is removed by only a short interval from the jugular vein 

 (fig. 12, Ot). 



In embryos of the pig 25 to 27 mm. in length, the cells compos- 

 ing the anlage of the otic ganglion have become more Compactly 

 aggregated and the entire ganglionic mass appears correspond- 

 ingly smaller and more closely associated with the nerve-trunk 

 (fig. 13, Ot). Many of the cells in the ganglion may now be 

 recognized as neuroblasts. The ganglion remains more or less 

 irregular in outline and from its posterio-ventral aspect a cord 

 of cells associated with a few fibers may be traced toward the 

 parotid gland. This condition was observed also in an embryo 

 of the cat 22 mm. in length. 



As in the case of the sphenopalatine ganglion, the cells which 

 constitute the earliest anlage of the otic ganglion are identical 

 in appearance with the cells in the semilunar ganglion. As devel- 



THE JOURNAL OF COMPARATIVE NEUROLOGT, VOL. 2.3, NO. 2 



