60 THE SKELETON OF THE HORSE 



foramen (Foramen incisivum). The alveolar border (Limbus alveolaris) separates 

 the palatine and labial surfaces; it is curved and thick, and presents three alveoli 

 for the incisor teeth ; behind the third alveolus it is rounded and free, forming part 

 of the interalveolar space. 



The nasal process (Processus nasalis) projects backward and upward from the 

 body, forming here the lateral wall of the nasal cavity. The two surfaces, facial 

 and nasal, are smooth and rounded. The superior border is free, thick, and smooth. 

 The inferior border is dentated and joins the maxilla; at its anterior end it forms 

 with the latter the alveolus for the permanent canine tooth. ^ The posterior 

 extremity fits into the interval between the nasal bone and the maxilla. 



The palatine process (Processus palatinus) is a thin plate which forms the an- 

 terior part of the basis of the hard palate. Its nasal or superior surface has a 

 longitudinal ridge which forms with that of the other side a groove for the septal 

 cartilage. The palatine or inferior surface is flat. The internal border is serrated 

 and meets its fellow at the median palatine suture. The external border is sep- 

 arated from the maxilla and the nasal process by the palatine cleft (Fissura pala- 

 tina). The posterior extremity fits into the interval between the vomer and the 

 palatine process of the maxilla. 



Development. — The premaxilla ossifies from a single center. Fusion of the 

 two bones is complete at the end of the third or the beginning of the fourth year. 



The Palatine Bones 



The palatine bones (Ossa palatina) are situated on either side of the posterior 

 nares, and form the posterior margin of the hard palate. Each is twisted so as to 

 form a horizontal and a perpendicular part. 



The horizontal part (Pars horizontalis) is a narrow plate which forms the pos- 

 terior part of the hard palate. It presents smooth nasal and palatine surfaces. 

 The internal border meets its fellow at the median palatine suture, on the nasal 

 aspect of which is the nasal crest. The anterior border joins the palate process of 

 the maxilla at the transverse palatine suture, and forms with it the anterior pala- 

 tine foramen. The posterior border is concave and free; it gives attachment to 

 the aponeurosis of the soft palate. 



The perpendicular part (Pars perpendicularis) is more extensive and forms the 

 outer boundary of the posterior nares. The nasal or internal surface is in the 

 greater part of its extent concave and smooth ; it is marked by a narrow rough area 

 to which the pterygoid bone is attached. Below this the bone curves outward, 

 forming the pterygoid process. The maxillary or external surface (Facies max- 

 illaris) presents three areas for consideration. The largest articulates with the 

 maxilla; it is rough and is crossed by a groove which enters into the formation of 

 the palatine canal. Behind this is a smooth part which assists in forming the 

 pterygo-palatine fossa. The rough area below this is overlapped by the pterygoid 

 process of the sphenoid bone. The superior border is perforated by the spheno- 

 palatine foramen. Behind the foramen the two plates of the bone separate to 

 inclose part of the spheno-palatine sinus. The inner plate curves inward to articu- 

 late with the vomer. The outer plate joins the maxilla and frontal and the orbital 

 wing of the sphenoid. 



Development. — The palatine bone ossifies in membrane from a single center. 



The Pterygoid Bones 



The pterygoid bones (Ossa pterygoidea) are narrow, thin, bent plates, situated 



on either side of the posterior nares. Each has two surfaces and two extremities. 



The internal surface is smooth, and forms part of the boundary of the posterior 



nares. The external surface articulates with the palatine, vomer, and sphenoid, 



' The alveolus for the temporary canine is commonly formed in the maxilla alone. 



