THE NASAL BONES. 



145 



(fuse at their lower edges, and by forward growth invade the posterior end of each 



[anterior paraseptal cartilage,, thus forming a deep groove in which the septal cartilage 



I is lodged (Fawcett). As growth goes on the groove becomes reduced by the further 



{ fusion of the lateral plates and the absorption of the cartilage, until the age of puberty, 



by which time the lateral laminae have united to form a median plate, the primitively 



divided condition of which is now only represented by the eversion of the alae and 



j the grooving along the anterior border. According to Fawcett, the ossification of the 



| Jacobsonian cartilage produces a hitherto undescribed element in the formation of the 



; osseous nasal septum. 



Ossa Nasal ia. 



The nasal bones, two in number, lie in the interval between the frontal 



processes of the maxillae, there forming the bridge of the nose. Each bone 



j is of elongated quadrangular form, 



I having two surfaces an inner and 



i outer and four borders. The outer 



surface, somewhat constricted about a 



its middle, is convex from side to a 



side, and slightly concavo-convex from J> 



above downwards. Near its centre ' | 



there is usually the opening of a 



nutrient canal. 



The inner surface is not so ex- 

 tensive as the outer, as the superior 

 and anterior articular borders encroach 

 somewhat upon it above. Concave 

 from side to side, and also from above 

 downwards, it is covered, in the recent 

 condition, by the mucous membrane of the nose. Eunning downwards along this 

 surface is a narrow groove (sulcus ethmoidalis) which transmits 'the anterior 

 ethmoidal nerve. The anterior or medial border, thin below, is thick above, 

 and, in conjunction with its fellow at the opposite side, with which it 

 articulates, forms a median crest posteriorly, which is united to the spine of the 

 frontal, the perpendicular plate of the ethmoid, and the septal cartilage of the nose, 

 in that order from above downwards. The posterior or lateral border, usually 

 the longest, is serrated and bevelled to fit on to the anterior edge of the frontal 

 process of the maxilla. The superior border forms a wide toothed surface, which 

 articulates with the medial part of the nasal notch of the frontal bone anteriorly ; 

 whilst, posteriorly, it rests in contact with the root of the nasal process of the same 

 bone. The inferior border is thin and sharp, and is connected below with the lateral 

 cartilage of the nose, and is usually deeply notched near its medial extremity. 



Connexions. The nasal bone articulates with its fellow of the opposite side, with the frontal 

 above, posteriorly with the perpendicular plate of the ethmoid and with the frontal process of the 

 maxilla. It is also united to the septal and lateral cartilages of the nose. 



Ossification. The nasal bones are each developed from a single centre, which 

 makes its appearance, about the end of the second month, in the membrane covering the 

 anterior part of the cartilaginous nasal capsule. Subsequent to birth the underlying 

 cartilaginous stratum disappears, persisting, however, below in the form of the lateral 

 nasal cartilage, and behind as the septal cartilage of the nose. 



B 



FIG. 156. THE RIGHT NASAL BONE. 

 A, Lateral side ; B, Medial side. 



Ossa Suturarum (O.T. Wormian). 



Along the line of the cranial sutures and in the region of the fontanelles, isolated 

 bones of irregular form and variable size are occasionally met with. These are the once so- 

 called Wormian bones, named after the Danish anatomist Wormius. They are now called 

 ossa suturarum (sutural bones). Their presence depends on the fact that they are either 

 developed from distinct ossific nuclei, or it may be from a division of. the primary ossific 

 deposit. Their occurrence may also be associated with certain pathological conditions 



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