THE NASAL BONES — THE LACRIMAL BONES 61 



concun-ing with the last in the formation of the pterygoid or Vidian canal. The 

 anterior extremity is free, turned shghtly outward, and forms the hamulus, 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, a base, and an apex. 



The external or facial surface is smooth and is convex transversely; the 

 profile contour is usually slightl}' wavy, with a depression about its middle and a 

 variably prominent area in front. 



The internal or nasal surface is smooth and concave from side to side. About 

 in its middle it presents the superior turbinal crest (Crista conchalis dorsalis), 

 which is parallel with the inner border, and has the superior turbinal bone attached 

 to it. Most of this surface faces into the nasal cavity, but its posterior part enters 

 into the formation of the frontal sinus; the latter area is marked off by an oblique 

 ridge. 



The internal border is straight, and meets the opposite bone at the nasal suture. 



The external border is irregular. Its anterior third is free and concurs with 

 the nasal process in forming the naso-maxillary notch (Incisura naso-maxillaris). 

 Behind this it is scaly for articulation with the end of the nasal process, the maxilla, 

 and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures. 



The base or posterior end is beveled and overlaps the frontal bone, forming the 

 naso-frontal suture. 



The apex is pointed and thin. 



Development. — Each nasal bone ossifies in membrane from a single center. 

 The nasal suture does not close completely even in old age. In some cases the two 

 plates separate to inclose a small air-space in the posterior part. 



The Lacrimal Bones 



The lacrimal bones (Ossa lacrimalia) are situated at the anterior part of the 

 orbit, and extend forward on the face to the posterior border of the maxilla. Each 

 presents three surfaces and a circumference. 



The external aspect is clearly divided into orbital and facial parts by the orbital 

 margin. The orbital surface (Facies orbitaHs) is triangular in outhne, smooth and 

 concave; it forms part of the inner and front wall of the orbit. Near the orbital 

 margin it presents a funnel-like fossa for the lacrimal sac (Fossa sacci lacrimalis), 

 which is the entrance to the osseous lacrimal canal. Behind this is a depression in 

 which the inferior oblique muscle of the eye takes origin. The facial surface 

 (Facies facialis) is more extensive, and has the form of an irregular pentagon. 

 It is slightly convex and smooth in the foal, flattened in the adult. It usually 

 bears the small lacrimal tubercle, situated nearly an inch (ca. 2 cm.) from the 

 orbital margin. 



The nasal or internal surface (Facies nasalis) faces into the frontal and max- 

 illary sinuses. It is concave and very irregular, and is crossed almost horizontally 

 by the osseous lacrimal canal (Canalis lacrimalis osseus). 



The orbital margin (Margo orbitalis) is concave, rough above, smooth below. 



The circumference articulates above with the frontal and nasal bones, below 

 with the malar and maxilla, in front with the maxilla, and behind with the frontal. 

 The various sutures so formed are designated by combinations of the names of the 

 bones. 



Development. — Each ossifies in membrane from a single center. 



