THE TEETH 35 



into any of the sinuses, causing sinusitis. If this occurs in the 

 frontal region, a dull pain is felt over the eyes; if in the ethmoid 

 region, a pain at the side of the nose and a change in the sound of 

 the voice (nasal tone) are noted. The inflammation frequently 

 extends into the antrum of Highmore. 



The sense of smell resides in the upper part of the nose, the 

 olfactory nerves coming down through the sieve-like plate of the 

 ethmoid bone in the roof of the fossa. 



BONES OF THE NECK 



Hyoid (os hy aides). 

 Seven cervical vertebrae. 



The hyoid bone, or os hyoides. Shaped like the letter U, 

 situated in front of neck, about on a level with the chin, and sus- 

 pended by ligaments and muscles from the styloid process of the 

 temporal bone. The hyoid is not articulated to any other bone. 

 It consists of a body and four cornua (or horns), and is designed 

 to give attachment to the muscles of the tongue, and to others 

 which connect it to the mandible above and sternum and clavicle 

 below. 



Seven cervical vertebrae. The seven cervical vertebrae and 

 their articulations will be described with the spinal column. 



THE TEETH 



A tooth is composed of dentine or tooth-bone, and consists 

 briefly of a crown, a. neck, and a root. 



Crown _____ a| _ 



. _,_ -Root 



Cusp- 

 Neck- 



HI cav " y H 



_ . 'Neck 



i / ii mi 



Qngulum. 

 "Crown 



FIG. 28. A MOLAR TOOTH IN SECTION AND A CANINE TOOTH. (Morris.) 



The crown is the exposed portion and is covered with hard 

 white enamel. The root (connected with the crown by the neck) 

 is concealed in the socket of the jaw and is covered with cement. 

 The shape of the tooth varies from that of the flat incisor or cutting 

 tooth, to the broad one for crushing and grinding. 



