NERVOUS SYSTEM OF A TWO-HEADED PIG EMBRYO 



383 



anterior limb buds was made in order to understand clearly the 

 morphological axes and planes of section. The model conforms 

 accurately to the external appearance of the teras already de- 

 scribed and figured (Wilder, '08; Bishop, '08), but to bring the 

 organism quickly before the reader Wilder's pen sketches have 

 been reproduced, and two drawings of the model added (figs. 

 1, 2, 3). 



Below the level of the shoulders the embryo appears exter- 

 nally as a single individual arising from one umbilical cord. The 

 head region, however, is partlj^ double. The snouts are separate 



Fig. 3 Three pen-and-ink sketches of the entire embryo made before it was 

 sectioned. (After H. H. Wilder.) 



and diverge at the same angle from the median plane of the organ- 

 ism, although the doubled head is twisted a little to the left, and 

 the right member (designated head A) is tilted downward slightly 

 more than the left (head B). Above and between the diverged 

 snouts there is a single palpebral opening in which are two sep- 

 arate eyeballs, the left eye of one member being approximated 

 to the right eye of the other. Because of the tilting of heads 

 A and B, the median eyes lie at a higher level than the outer eyes. 

 The outer sides of the teratological head appear normal in every 

 respect (figs. 2, 3). Below these median eyes and between the 

 diverged snouts is a broad area which externally has little to com- 

 mend it to the reader's attention, but internally its anatomy 

 showed it to be one of the most interesting regions of the entire 



