PLATE LVII . 



Balcenoptera boratlix. 



Fig. 1. 

 Fig. 2. 

 Fig. 3. 

 Fig. 4. 



Left mandible, lateral view. Twice natural size. 

 Left mandible, mesal view. Twice natural size. 

 Left otic capsule and auditory ossicles, ventral view. 

 Cervical vertebra;, ventral view. 3 X natural size. 



4 X natural size. 



1. M temporalis. 



2. M. masseter, deep portion. 



3. M. masseter, superficial portion. 



4. M. depressor mandibulae (M. digastricus, posterior belly). 



5. M. digastricus, anterior belly. 



6. M. pterygoideus interims. 



7. M. mylohyoideus. 



8. Meckel's cartilage. 



9. Lingula. 

 10. Malleus. 



11. Incus. 



12. Stapes. 



13. M. stapedius. 



14. Canalis facialis. 



15. Canalis semicircularis externus. 



16. Tegmen tympani. 



17. Cochlea. 



18. M. tensor tympani. 



19. Foramen, conducting vessels to the interior of the cochlea. 



