THE PTERYGOID BONES—THE NASAL BONES . 67 
The perpendicular part (Pars perpendicularis) is more extensive and forms 
most of the lateral wall of the choanz or posterior nares. The nasal surface (Facies 
nasalis) is in the greater part of its extent concave and smooth, but presents a 
narrow rough area to which the pterygoid bone is attached. Below this the bone 
curves outward, forming the pterygoid process. The maxillary surface (Facies 
maxillaris) presents three areas for consideration. The largest articulates with the 
maxilla; it is rough and is crossed by a groove which concurs with one on the max- 
illa in the formation of the palatine canal. Behind this is a smooth part which 
assists in forming the pterygo-palatine fossa (Fossa pterygopalatina). The rough 
area below this is overlapped by the pterygoid process of the sphenoid bone. The 
dorsal border is perforated by the sphenopalatine foramen. Behind the foramen 
the two plates of the bone separate to inclose part of the sphenopalatine sinus. 
The inner plate curves medially to articulate with the vomer. The outer plate 
joins the maxilla and frontal and the orbital wing of the sphenoid; it may join the 
lacrimal bone also. 
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 medial surface is smooth, and forms part of the wall of the posterior nares. 
The lateral surface articulates with the palatine, vomer, and sphenoid, concurring 
with the last in the formation of the pterygoid canal. The ventral extremity is 
free, turned slightly outward, and forms the hamulus pterygoideus; this is grooved 
externally and forms a pulley around which the tendon of the tensor palati muscle 
is reflected. 
Development.—The pterygoid ossifies in membrane from a single center. 
THE NaSAL BONES 
The nasal bones (Ossa nasalia) are situated in front of the frontal bones and 
form the greater part of the roof of the nasal cavity. They have an elongated 
triangular outline, wide behind, pointed in front. Each presents two surfaces, two 
borders, and two extremities. 
The facial surface is smooth and is convex transversely; the profile contour is 
usually slightly wavy, with a depression about its middle and a variably prominent 
area in front. 
The nasal surface is smooth and concave from side to side. About in its 
middle it presents the dorsal turbinate crest (Crista turbinata dorsalis), which is 
parallel with the medial border, and has the dorsal turbinate bone attached to it. 
Most of this surface faces into the nasal cavity, but its posterior part, lateral to 
the turbinate crest, enters into the formation of the frontal sinus; the latter area is 
marked off by an oblique ridge which corresponds to the septum between the an- 
terior and posterior parts of the dorsal turbinate bone. 
The medial border is straight, and meets the opposite bone at the nasal suture. 
The lateral border is irregular. Its anterior third is free and concurs with 
the nasal process of the premaxilla in forming the naso-maxillary notch (Incisura 
naso-maxillaris). Behind this it joins the end of the nasal process, the maxilla, 
and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures. 
The greater part of the edge is beveled and fits into a groove on the upper border of the 
nasal process, the maxilla, and the lacrimal bone. 
The posterior extremity or base is beveled and overlaps the frontal bone, 
forming the naso-frontal suture. 
The anterior extremity or apex is pointed and thin. 
