ANATOMY IN A NUTSHELL. 541 



Insertion. — Into the upper lip blending with the Orbicularis oris. 



Action. — To elevate the lip. 



Nerve Supply. — Infraorbital branch of the facial. 



Blood Supply. — Facial. 



LESSON CLXXXIII. 



Inferior Maxillary Honk. (Plates CCLVI-CCLVII). 



The inferior maxillary bone consists of a body shaped something like a 

 hi nvs shoe with the ends spread, and two vertical rami which meet the body at 

 nearly a right angle. The body has the following points for consideration: 



The external surface of the body is convex from side to side. bu1 concave 

 from above downward. The symphysis is a vertical ridge in the middle line 

 marking the junction of the two lateral portions of the bone. The mental pro- 

 cess is a prominent triangular eminence which forms the chin. The incisive 

 fossa is situated on each side of the symphysis just below the incisor teeth, ami 

 jives origin to the Levator menti muscle. The Orbicularis oris has an origin 

 just externally from this fossa. The mental foramen is jusl below the interval 

 between the bicuspid teeth and is for the passage of the mental vessels and 

 nerve. The external oblique line passes outward from the base of the mental 

 process for a short distance, then passes upward and finally become- continu- 

 ous with the anterior border of the ramus. This line gives origin to the De- 

 pressor labii inferioris and the Depressor anguli oris muscles, while just below 

 it is attached the Platysma myoides. There is a groove near the anterior 

 inferior border of the Masseter muscle for the facial artery. 



The internal surface of the body is concave from side to side and convex 

 from above downward, just the reverse of the external surface. It has the 

 following points for consideration: 



A depression in the mid-line corresponding to the symphysis. The genial 

 tubercles or mental spin-'- are in two pairs and are situated just below the center 

 of this depression on either side. The upper pair give attachment to the 

 Eenio-hyo-glossi, and the lower pair give attachment to the Genio-hyoidei. 

 The sublingual fossa, which is for the sublingual gland, is external to these 

 tubercles on either side. Beneath this sublingual fossa at the lower margin of 

 the bone is the digastric fossa, which gives attachment to the Digastric muscle. 

 The mylo-hyoid ridge passes obliquely upward and outward and gives attach- 

 ment to the Mylo-hyoid muscle. The posterior extremity of this ridge gives 

 attachment to the Superior constrictor muscle and the pterygo-maxillary liga- 

 ment. The submaxillary fossa, which b for the submaxillary gland, is below 

 the mylo-hyoid ridge. These oblique line- mi the external surface and the in- 

 ternal surface divide the body into an upper and a lower portion. 



The superior border of the body, or aveolar border. i> thick behind and has 

 on each side eighl cavities for the teeth, h gives attachment to the Buccinator 

 muscle on its external surface behind the first molar tooth. 



The inferior border is longer than the superior border and is thicker an- 

 teriorly which is just the reverse of the superior border. A groove for the 



