ENDOSKELETON. ANIMALS. 45 



with audition. The frontal sinuses give lightness to the 

 bone and protection to the brain ; the antrnm making the 

 superior maxilla light. 



A. 200. Cranium of a Cat. (Felis domestica). Red bristles 

 have been passed in the direction of the Eustachian tubes 

 into the tympana. A black bristle from the left frontal 

 sinus through a curved passage to its opening in the 

 middle meatus of the nose. A green bristle from the left 

 sphenoidal cell formed in the presphenoid into the postero- 

 inferior region of the nose. The tympanic element of the 

 temporal bone has given origin by its entotympanic portion 

 to a large tympanic bulla partly separated by a bony septum 

 from the true tympanum. 



A. 201. The two halves of a transverse section of a Cat's cranium 

 (Felis domestica). Similar bristles have been introduced 

 into the air-containing chambers. 



A. 202. Left half of a Human cranium, similarly treated ; a white 

 bristle has also been passed into the mastoid cells. 



A. 203. Transverse section of a Human cranium. The frontal 

 and maxillary air-chambers are shown. 



