NERVOUS SYSTEM OF A TWO-HEADED PIG EMBRYO 413 



(also fused). This appears in section 242 (fig. 15) as a winged 

 mass equidistant from the basis cranii and nasal septa of the 

 two snouts. It is shown in relation to the basis cranii in section 

 232 (fig. 14). 



Two other important landmarks have already been mentioned. 

 These are the sphenopalatine gangha of the median region, not 

 fused, but independent for each moiety of its respective head 

 (figs. 13, 14, 15). 



In summary, the following anatomical landmarks have been 

 estabhshed in the median region between the two snouts, external 

 to the brain: 1) non-conjoined or independent structures- 

 parotid glands, developing ducts of submaxillary and sublingual 

 glands, masseter and external pterygoid muscles, sphenopalatine 

 ganglia; 2) conjoined structures (i.e., contributions from the 

 left half of head A and the right half of head B)— a submaxillary 

 and sublingual terminus, Meckel's cartilage (otic ends), cartilage 

 of the external auditory meatuses, periotic cartilage of the middle 

 ears, cartilagenous capsule of the internal ears. All are con- 

 siderably reduced in size, as might be expected from the limited 

 space into which they have been cramped. 



With these landmarks in mind, the identity of the median 

 isolated ganglion may be satisfactorily estabhshed. The gan- 

 ghon itself is sUghtly flattened and hes close to, but not touching, 

 the conjoined internal ear capsules. If the ''two pairs of nerves 

 that proceed from its lateral borders" be traced peripherally 

 they are seen not to ''lose themselves in the surrounding tissues," 

 but to pursue a definite, recognizable course. The 'anterior 

 ones' lead directly into the sphenopalatine gangha of the median 

 region; the 'posterior ones' course rostrally around the cartilages 

 of the nasal capsule of each snout to the upper hp (figs. 14 to 

 16). In addition there emerge from the under surface of the 

 ganghon two slender nerve strands which descend parallel to 

 each other for a very short distance, then separate, sending a 

 branch to either side of the median periotic cartilage, and some- 

 what rostral to the fused otic ends of Meckel's cartilages each 

 turns beneath the external pterygoid muscle toward the oral 

 cavity of its respective head (figs. 15 to 17). All the morpho- 



