82 INFERIOR MAXILLARY BONE. 



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

 various periods of life ; thus, in the fcetus and infant, it is almost parallel 

 with the body ; in youth it is oblique, and it gradually approaches the ver- 

 tical direction until manhood ; in old age, after the loss of the teeth, it 

 again declines and assumes the oblique direction. Upon its external sur- 

 face it is rough, for the attachment of the masseter muscle ; and at the 

 junction of its posterior border with the body of the bone is a rough tuber- 

 osity, the angle of the lower jaw, which gives attachment by its inner 

 margin to the stylo-maxillary ligament. 



-p jo . 38 The upper extremity of the ramus pre- 



sents two processes, separated by a con- 

 cave sw r eep, the sigmoid notch. The an- 

 terior is the coronoid process ; it is sharp 

 and pointed, and gives attachment by its 

 inner surface to the temporal muscle. 

 The anterior border of the coronoid pro- 

 cess is grooved at its lower part for the 

 buccinator muscle. The posterior pro- 

 cess is the condyle of the lower jaw, which 

 is flattened from before backwards, oblique 

 in direction, and smooth upon its upper 

 surface, to articulate with the glenoid ca- 

 vity of the temporal bone. The constriction around the base of the con- 

 dyle is its neck, into which is inserted the external pterygoid muscle. The 

 sigmoid notch is crossed by the masseteric artery and nerve. 



The internal surface of the ramus is marked near its centre by a large 

 oblique foramen, the inferior dental, for the entrance of the inferior dental 

 artery and nerve into the dental canal. Bounding this opening is a sharp 

 margin, to which is attached the internal lateral ligament, and passing 

 downwards from the opening a narrow groove which lodges the mylo- 

 hyoidean nerve with a small artery and vein. To the uneven surface 

 above, and in front of the inferior dental foramen, is attached the temporal 

 muscle, and to that below it the internal pterygoid. The internal surface 

 of the neck of the condyle gives attachment to the external pterygoid 

 muscle ; and the angle to the stylo-maxillary ligament. 



Development. By two centres : one for each lateral half, the t\vo sides 

 meeting at the symphysis, where they become united. The lower jaw is 

 the earliest of the bones of the skeleton to exhibit ossification, with the 

 exception of the clavicle ; ossific union of the symphysis takes place during 

 the first year. 



Articulations. With the glenoid fossae of the tw r o temporal bones, 

 through the medium of a fibro -cartilage. 



Attachment of Muscles. To fourteen pairs : by the external surface, 

 commencing at the symphysis and proceeding outwards, levator labii 

 inferioris, depressor labii inferioris, depressor anguli oris, platysma myoides, 



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

 <or the depressor labii inferioris muscle. 5. The mental foramen. 6. The external 

 oolique ridge. 7. The groove for the facial artery ; the situation of the groove is marked 

 by a notch in the bone a little in front of the number. 8. The angle. 9. The extremity 

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

 3'gmoid notch 13. The inferior dental foramen. 14. The mylo-hyoidean groove. 10, 

 The alveolar process, t. The middle and lateral incisor tooth of one side. t. The c;i- 

 tune tooth. 6. The two bicuspides. m. The three molares. 



