30 HUMAN ANATOMY. 



The ramus or horizontal portion on either side is somewhat 

 quadrilateral, and presents the following points: 



The internal surface of ramus; 



Foramen of inferior dental canal, for inferior dental vessels 

 and nerve; 



Mylo-hyoidean groove, described above; 



Spine, for attachment of the internal lateral ligament of 

 the lower jaw. 



The upper border is surmounted by two processes, the coro- 

 noid and the condyloid processes, separated by the sigmoid notch. 



The coronoid process is in front, and affords attachment for 

 the temporal muscle. 



The condyloid process articulates with the glenoid fossa of 

 the temporal bone, being supported upon a constricted portion, 

 the neck, which receives the insertion of the external pterygoid 

 muscle, and presents to its outer side a tubercle for the external 

 lateral ligament of the lower jaw. 



The sigmoid notch is crossed by the masseteric vessels and 

 nerve. 



The lower border presents : 



Angle of the jaw, the point of junction of the ramus with 

 the body; 



Rough surface, for attachment of the stylo-maxillary liga- 

 ment, and on its inner side the internal pterygoid muscle, and 

 on its outer side the masseter. 



It articulates with the two temporal bones. 



The muscular attachments are fifteen pairs ; to the external 

 surface, six depressor anguli oris, depressor labii inferioris, 

 levator labii inferioris, orbicularis oris, platysma myoides, and 

 buccinator; from the internal surface of the body, five the 

 genio-hyoglossus, genio-hyoid, mylo-hyoid, digastric, and supe- 

 rior constrictor; and to the ramus, four the masseter, internal 

 and external pterygoid s, and temporal. 



It has two ossific centres, one for each lateral half, devel- 

 oped partly from membrane, partly from cartilage, being pre- 

 ceded in time only by one bone the clavicle. 



Changes in Lower Jaw. Certain changes occur in the size 

 and shape of the lower jaw as age advances. 



At birth the body is shell-like, containing sockets for the 

 ten temporary teeth, the mental foramen is large and opens 

 beneath first molar, and the coronoid process is large and at right 

 angles to base. 



In adults the base and alveolar process are equal in size, 

 the mental foramen opens midway between upper and lower 

 borders, and the rami are at nearly right angles to base. 



