NASAL CAVITIES 395 



existed in the embryo between the cavities of the nose and the 

 mouth. 4 



Lateral Wall of the Nasal Cavity. The lateral wall of 

 the nasal cavity is rendered uneven and complicated by the 

 projection of the three conchae (O.T. turbinal bones). 



The part which the different bones take in the formation of the lateral 

 wall of the cavity of the nose must in the first place be studied in a 

 sagittal section through the macerated skull, and the dissector should 

 constantly refer to such a preparation during the dissection. Anteriorly, it 

 is formed by the lateral cartilage, the alar cartilage, the nasal bone, and the 

 frontal process of the maxilla. More posteriorly the lacrimal, the ethmoid, 

 and the inferior concha, with a small portion of the body of the maxilla, 

 enter into its construction ; whilst still more posteriorly are the perpen- 

 dicular part of the palate bone and the medial pterygoid lamina of the 

 sphenoid. Placed in relation to the lateral aspect of this wall are the 

 ethmoidal air-cells, which intervene between the upper part of the nasal 

 cavity and the orbit, whilst, at a lower level, the great air sinus of the 

 maxilla, the maxillary sinus, is situated immediately to the lateral side of 

 the nasal cavity (Fig. 154). 



Turning now to the dissection, the dissector will see that 

 the lateral wall is separable into three areas or districts. 

 These are (i) the vestibule; (2) the atrium meatus medii ; 

 (3) the region of the conchae and the intervening meatuses. 



Vestibulum Nasi. The vestibular part (Fig. 155, e, e') 

 of the lateral wall is a depression of a somewhat oval form 

 placed immediately above the aperture of the nostril. It is 

 partially divided into an upper and lower portion by a short 

 ridge, which projects anteriorly from its posterior boundary ; 

 and it is clothed throughout with integument continuous with 

 the skin. From this a number of stout, stiff hairs, termed 

 vibrissce, project (Fig. 155, 5 ). The vibrissae which spring 

 from the anterior part of the region incline posteriorly, whilst 

 those which are implanted into the posterior part are directed 

 anteriorly ; in this manner a sieve-like arrangement is provided 

 at the anterior aperture of the nose. The vestibular part of 

 the lateral wall is placed opposite the corresponding area on 

 the septum nasi, and the two together constitute an ampullated 

 entrance to the nasal cavity. The capacity and shape of this 

 section of the cavity is influenced to a certain extent by the 

 contraction of the nasal muscles. 



Atrium Meatus Medii. This part of the lateral wall of the 

 nasal cavity (Fig. 155, s) is placed above, and slightly posterior 

 to the vestibular district, and it receives its name from the 

 fact that it lies immediately anterior to the middle meatus. 



