52 BONES OF THE HEAD. 



muscle. The internal surface presents at its middle the inferior dental 

 foramen, leading into the dental canal, which lodges the dental nerve 

 and vessels. Passing down from the sharp inferior margin of this foramen 

 is the mylo-hyoid groove (occasionally a canal for a short space), marking 

 the passage of the mylo-hyoid nerve with an accompanying artery and 

 vein. Behind this, inside the angle, 13 a marked roughness for the internal 

 pterygoid muscle. 



Each ramus is surmounted by two processes, the condyle and the coro- 

 noid, which are separated by a deep excavation, the sigmoid notch. The 

 condyle is continued upwards from the posterior part of the ramus. It is 

 supported by a constricted portion, the neck, which presents anteriorly a 

 depression, into which the external pterygoid muscle is inserted. The con- 

 dyle is a transversely elongated convex articular process, whose major axis 

 is directed obliquely, so that if prolonged it would meet with that of its 

 fellow near the anterior margin of the foramen magnum. The coronoid 

 process is continued vertically upwards in front, from the anterior margin of 

 the ramus. It is pointed, and gives attachment by its margin and inner 

 aspect to the temporal muscle. At its base, in front, is a groove, to which 

 the buccinator muscle is attached. 



The anterior margin of the ramus is placed at nearly a right angle to the alveolar 

 border. The angle of the jaw, which is the meeting of the posterior border of 

 the ramus with the base, is in the adult usually about 120 ; in infancy it is as 

 great as 140 or more ; in strongly developed jaws it may be diminished to 110 or less ; 

 and in old and toothless jaws it is increased. These changes are connected with a 

 variety of circumstances, among which may be noticed, the development of the 

 temporary and permanent teeth, the absorption of the alveolar arch in advanced age, 

 the elongation of the face and upper jaw towards adult life, and the varying state of 

 development of the masseter muscles at different periods. 



THE HYOID BONE. 



The hyoid bone, or os linguae,, is situated at the base of the tongue, and 

 may be felt between the chin and the thyroid cartilage. It is suspended 

 from the tips of the styloid processes of the temporal bones by a pair of 

 slender bands, the stylo-hyoid ligaments, which are osseous in most animals. 

 Hence, though not strictly a bone of the cranium or face, it properly falls 

 to be considered in this place. It is shaped like the letter u, and consists 

 of a body and two pairs of cornua. 



Fig. 47. Fig. 47. THE HYOID BONE, FROM BEFORE, f 



1, the prominent part of the body ; 2, the great cornu ; 

 3, the lesser cornu. 



The lody, or central piece, is compressed from 

 before backwards, and lies in a plane, directed 

 downwards and forwards. Its anterior surface is 



convex, and marked in the middle by a vertical ridge, on each side of which 

 are depressions for the attachment of muscles. Its posterior surface is 

 concave, and is directed towards the epiglottis. 



The great cornua project backwards from the sides of the body, and end 

 in rounded extremities. 



The small cornua, or cornicula, short and conical, project upwards and 

 backwards from the place of junction of the body with the great cornua, 



