KESPIKATIOK 453 



by its external or free border to the outer wall of the cavity. 

 Each turbinated bone contains two cavities internally, an 

 anterior and posterior, separated from each other by a median 

 plate, and communicating respectively with the middle meatus, 

 and the maxillary or frontal sinuses. Projecting into the 

 posterior part of each chamber are the ethmoid cells a col- 

 lection of small horn-like structures, formed of thin laminae, 

 rolled upon themselves, and resembling turbinated bones in 

 miniature. Still another set of cavities communicate with 

 the nostril the sinuses. These are irregular interspaces 

 between the superficial and deep plates of the facial bones, 

 opening into one another, and into the nasal chamber. They 

 are three in number on each side, the frontal, the sphenoidal, 

 and the maxillary. The frontal is situated between the eyes, 

 and extends as far forwards as the nasal bones ; the sphenoid 

 is deeply situated in front of the cranium and beneath the 

 frontal, with which it communicates; the maxillary is placed 

 immediately above the molar teeth of the upper jaw, and ex- 

 tends from the level of the eye to the third molar tooth. 

 These spaces are small in very young animals, and gradually 

 increase with advancing age. In oxen they are very capaci- 

 ous, covering the whole front of the cranium, and extending 

 into the horns. In carnivora, on the other hand, they are 

 very restricted. The osseous and cartilaginous walls of the 

 nostrils, and the various contiguous cavities the false nostril 

 of the horse excepted are covered by mucous membrane, 

 formed of a somewhat lax layer of connective tissue, covered 

 by a basement membrane and epithelial cells. In each 

 chamber and communicating cavities, with the exception of 

 the posterior part of the former, these cells are columnar, and 

 the superficial layer is provided with vibratile ciliae, the con- 

 stant movements of which serve to clear the passages of 

 mucus and other matters. On the ethmoid cells, and the 



