424 MABEL BISHOP 



fibers, in so far as they could be followed. In the median region 

 tha course of the fibers is complicated by the altered form rela- 

 tions of the quadrants and the resulting topographical adjust- 

 ments to size and shape. Nevertheless, the normal pattern is 

 clearly recognizable and the following central connections are 

 demonstrable : The motor roots of the two facial nerves from the 

 genu internum to the rostral cranial nerve-mass (figs. 10, 11); 

 with some uncertainty, the sensory roots and the motor nucleus 

 of the conjoined trigeminus (fig. 9) and the acoustic fibers (fig. 9). 



21. Heads A and B have each a median raphe with a clearly 

 demonstrable sulcus limitans on either side of it as in a normal 

 embryo (figs. 9, 10). 



22. The fiber tracts of the outer sides are normal and readily 

 identifiable, e.g., the tractus spinalis trigemini (figs. 11 to 15), 

 tractus solitarius (figs. 11 to 13), and the fasciculus longitudinahs 

 medialis (figs. 9 to 12). In the median region the fiber tracts 

 are complicated by the altered form relations of the quadrants, 

 as are the intracranial nerve fibers, but again, the normal pattern 

 is recognizable through the teratological alterations. A greatly 

 reduced spinal fifth tract is identifiable for the inner half of each 

 head component for a considerable distance (fig. 9) . A fasciculus 

 longitudinahs medialis on each side of the median raphe of each 

 head member is demonstrable for a long distance before fusion 

 in the midline of the monster (figs. 9 to 15). This fusion adds 

 another definite landmark of union of the two heads, for the two 

 organisms are separate just as far as the fasciculi londitudinales 

 mediales are separate. A conjoined tractus solitarius is demon- 

 strable in the midline of the united dorsal quadrants in the con- 

 joined medulla (figs. 13, 14, 15). The cerebral peduncles and 

 posterior commissures are normal. 



23. Summary of the conjoined structures: Rhombencephalon 

 (figs. 5, 6, 8), fourth ventricle (figs. 9, 10), rostral and caudal 

 cranial nerve-masses (figs. 5, 6, 9 to 14), median gasserian gan- 

 ghon (fig. 10), median abducens nerve (not figured), median 

 ninth, tenth, eleventh, and twelfth nerves (fig. 5), median spinal 

 nerves (figs. 5, 18, 19, 20), median isolated geniculate ganghon 

 (figs. 5, 6, 14), median tractus sohtarius (figs. 13, 14), median 



