THE SKELETAL SYSTEM 23 



Palatine, or Palate, Bone (Os Palatinum) 



The palatine bone, membranous in origin, consists 

 chiefly of three elements — the horizontal part, and the orhi- 

 tal and sphenoidal processes. The horizonal part consti- 

 tutes the posterior region of the hard palate, and there- 

 fore is the ventral boundary of the choana. It meets its 

 fellow of the opposite palatine bone at the median suture 

 along the dorsal side of the mouth cavity. Laterally it 

 articulates with the alveolar process of the maxillary bone. 

 The orbital process, which joins the horizontal part nearly 

 at right angles, is exposed to the orbito-temporal fossa. 

 It constitutes the greater part of the nasopharyngeal duct 's 

 lateral wall. The dorsal edge articulates with the pre- 

 sphenoid bone. The sphenoid process extends backward 

 to the pterygoid process, and joins dorsally an anterior 

 extension of the alisphenoid bone. 



The Mandible (Mandibula) 



The mandible comprises two lateral elements united in 

 front by connective tissue at the mandibular symphysis. 

 Each element contains five parts: the body, the ramus, 

 and three processes attached to the latter posteriorly. The 

 body of each half of the mandible is prolonged anteriorly 

 as a strong, curved process bearing one large incisor tooth. 

 This tooth projects anterodorsally a considerable distance 

 beyond the bone. Behind the incisor is the diastema, a 

 toothless region corresponding to the diastema of the upper 

 jaw. A row of three molar teeth is posterior to the dia- 

 stema. The two rows of molars are approximately parallel 

 to each other, but each row forms an acute angle with the 

 long axis of the bone in which it is inserted. There are 

 transverse ridges on the grinding surfaces of the molars. 

 The ramus is the laterally flattened region immediately 



