io8 A MANUAL OF ANATOMY 



The bone receives its blood-supply from the angular branch of 

 the facial, and the nasal and anterior ethmoidal branches of the 

 ophthalmic, arteries. 



Articulations. — ^The nasal articulates with four bones, as follows : 

 superiorly with the frontal, externally with the superior maxilla, 

 internally with its fellow, and posteriorly with the ethmoid and again 

 with the frontal. 



Structure. — The bone is composed of compact tissue, and is there- 

 fore dense. 



Ossification. — The nasal is developed in membrane from one centre, which 

 appears about the eighth week of intra-uterine life. 



The Lachrymal Bones. 



The lachrymal or tear-bone is situated at the anterior part of the 

 inner wall of the orbit, where it lies behind the nasal process of the 

 superior maxilla, and in front of the os planum of the ethmoid. It 

 is very thin and scale-like. From its resemblance in this sense 

 to a finger-nail, it is known as the os unguis. It is quadrilateral 

 and presents two surfaces and four borders, the inferior border 

 being recognised by its presenting a hamular and a descending pro- 

 cess. The external or orbital surface is traversed by the lachrymal 

 crest, which is nearer the anterior than the posterior border, and 



divides the surface into two unequal 

 Superior Border parts. The anterior division, represent- 



I ing one- third, presents the lachrymal 



groove, which lodges the lachrymal sac 

 L... Anterior Border and the Commencement of the nasal 



Lachrymal Groove duct. The loWCr CUd of this divisiOU is 



Orbital Surface prolonged into the descending process, 



,-- Hamular Process which takcs part in the wall of the lach- 



Descending Process j-ymal canal, and articulates with the 



Fig. 66.-THE Right Lack- |?^^7"'^lr^P'°i^'' °^ ^^f- ^"^'"°' *^^- 

 RYMAL Bone (External bmate. Ihe posterior division, repre- 

 ViEw). senting two-thirds, is smooth and forms 



part of the inner wall of the orbit. The 

 lachrymal crest gives origin to the tensor tarsi muscle, and 

 inferiorly terminates in a hook-like projection, called the hamular 

 process. This process is curved in a forward direction, and is 

 received into the lachrymal notch at the front part of the internal 

 border of the orbital plate of the superior maxilla, where it 

 bounds externally the superior orifice of the lachrymal canal. It 

 articulates with the lachrymal tubercle of the superior maxilla. 

 The internal surface presents a vertical furrow corresponding with 

 the position of the lachrymal crest on the external surface. 

 Superiorly it articulates with the front part of the lateral mass 

 of the ethmoid, where it helps to close ethmoidal cells, and forms 

 part of the infundibulum. Inferiorly it forms part of the outer 

 wall of the nasal fossa, and looks into the middle meatus. 



