Fig. 20 Cross section tlirough the posterior portion of the orbito-temi)or^J 

 region of an embryo having a carapace 13.5 mm. long, showing the pterygoideum 

 {pt.) extending medially beneath the arteria carotis interna (a.c.i.) and the ramus 

 palatinus n. facialis {r.p.) to form the sulcus cavernosus of the adult pterygoi- 

 deum. A thin osseous lamella maj' also be seen along the ventral crest of the 

 planum basale which extends further forward and fuses with theparasphenoi- 

 deum in the i-egion of the fenestra hypophyseos. X 15. 



Fig. 21 Cross section through the otic region of an embryo having a carai)ace 

 length of 7 mm. showing the columella auris (col.) in its relation to the first vis- 

 ceral cleft (1) to the ramus hyomandibularis n. facialis (r.h.), and to the chorda 

 tympani (c.t.). The processus interhyalis (pr.i.) in its relation to the cartilago 

 Meckelii (c.M.) is shown. X 15. 



Fig. 21 a A portion of figure 21 mure highly magnified. X 35. 



773 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 4 



