52 



INFERIOR MAXILLARY BONE. 



inferioris muscle; and corresponding with the root of the lateral 

 incisor tooth, another depression, the incisive fossa, for the levator 

 labii inferioris. Further outwards is an oblique opening, the 

 anterior mental foramen, for the exit of the inferior dental nerve 

 and artery, and below this foramen, an oblique ridge which gives 

 attachment to the depressor anguli oris, and platysma myoides. 

 Near the posterior part of this surface is a rough impression made 

 by the masseter muscle ; and immediately in front of this impres- 

 sion, a groove may occasionally be sepn for the facial artery. The 

 projecting tuberosity at the posterior extremity of the lower jaw, at 

 the point where the body and ramus meet, is the angle. 



Upon the internal surface of the body of the bone at the symphysis, 

 are two small pointed tubercles; immediately beneath these, two 

 other tubercles less marked and pointed, beneath them a ridge, and 

 beneath the ridge a rough depression of some size. These four 

 points give attachment from above downwards to the genio-hyo- 

 glossi, genio-hyoidei, part of the mylo-hoidei and to the digastric 

 muscles. Running outwards into the body of the bone from the 

 above ridge, is a prominent line, the mylo-hyoidean ridge, which 

 gives attachment to the mylo-hyoideus muscle, and by its extremity 

 to the pterygo-maxillary ligament and superior constrictor muscle. 

 Immediately above the ridge, and by the side of the symphysis, is a 

 smooth concave surface, which corresponds with the sublingual 

 gland; and below the ridge, and more externally, a deeper fossa for 

 the submaxillary gland. 



The ramus is a strong square-shaped process, differing in direc- 

 tion at various periods of life; thus, 

 in the fetus and infant, it is almost 

 parallel with the body ; in youth it 

 is oblique, and gradually increases 

 in the vertical directioR until man- 

 hood ; in old age, after the loss of 

 the teeth, it again declines and 

 assumes the oblique direction. 

 Upon its external surface it is 

 rough, for the attachment of the 

 masseter muscle ; and at the junc- 

 tion of its posterior border with the 

 body of the bone, is a rough' tube- 

 rosity, the angle of the lower jaw, 

 which gives attachment by its inner margin to the stylo-maxillary 

 ligament. 



The upper extremity of the ramus presents two processes, sepa- 

 rated by a concave sweep, tlje sigmoid notch. The anterior is the 



* The lower jaw. 1. The body. 2. The ramus. 3. The symphysis. 4. The 

 fossa for the depressor labii inferioris muscle. 5. The mental foramen. 6. The external 

 oblique ridge. 7. The groove for the facial artery. 8. The angle. 9. The extremity 

 of the mylo-hyoidean ridge. 10. The coronoid process. 11. The condyle. 12. The 

 sigmoid notch. 13. The inferior dental foramen. 14. The mylo-hyoidean groove. 

 15. The alveolar process, i. The middle and lateral incisor tooth of one side. c. The 

 canine tooth, b. The two bicuspides. m. The three molares. 



Fig. 22* 



