NERVOUS SYSTEM OF A TWO-HEADED PIG EMBRYO 423 



15. The line of fusion of the two brains is thus determined to 

 be along the external surface of the conjoined dorsal quadrants, 

 which is also the median sagittal plane of the monster. 



16. Twelve pairs of cranial nerves are present in normal 

 linear arrangement on the outer sides of the teratological head 

 (fig. 4). Only those branches which have relationship with the 

 median region are considered in this paper. 



17. Along the midline of the ventral surface of the conjoined 

 rhombencephalon there are two cranial nerve-masses, spatially 

 separated from each other and from the spinal neural ridge, and 

 attached to the brain by bundles of nerve-root fibers (figs. 5, 6, 

 9 to 12). The more rostral one is concerned with median cranial 

 nerves five, six, seven, and eight, and is designated the rostral 

 cranial nerve-mass; the other is concerned with median cranial 

 nerves nine, ten, eleven, and twelve, and is termed the caudal 

 cranial nerve-mass. 



18. The nerves of the median area are identified in part by 

 their superficial origins and peripheral distributions, in part by 

 their central connections. Nerves one, two, three, and four are 

 not involved in the teratological considerations. The nerves 

 identified by their central connections are given under paragraph 

 20. Those identified by their peripheral distributions are: a 

 conjoined gasserian ganglion with attached ophthalmic nerve 

 and its nasocihary infratrochlear branches to each head; con- 

 joined abducens nerve to the external recti muscles of the median 

 eyes; a conjoined geniculate ganghon (the median isolated gan- 

 ghon) with a pair of great superficial petrosal and chorda tympani 

 nerves, the infraorbital branches of the seventh nerve; median 

 glossopharyngeus (?); median vagus, accessory, and hypoglossus 



19. The median isolated ganglion is identified with the seventh 

 nerve, and not with the ninth or tenth as was suggested by 

 Wilder ('08). The anatomical evidence establishes its identity 

 as a conjoined geniculate ganghon (figs. 6, 14). 



20. The central connections of the cranial nerves could not 

 be determined in full. On the normal sides of the head there is 

 no indication of abnormal behavior of the intracranial nerve 



