DEVELOPMENT OF THE NOSE. 1429 



restricted avenue of approach through the nasal fossa. The chief obstacle is the 

 middle turbinate bone, which must be removed before the orifice can be seen or the 

 anterior wall removed. Any efforts at cleaning pathological tissue from the sinus 

 must be made with due regard for the important structures just outside and the thin 

 intervening bone. 



Inflammation of the ethmoidal cells is most frequently associated with the 

 presence of myxomatous polypi within the nose. Infection may extend (a) upward 

 to the cranial cavity, either directly or by way of the ethmoidal veins, or into the 

 cavernous sinus via the ophthalmic vein, or to the longitudinal sinus especially in 

 children by the small vein traversing the foramen caecum ; () outward to the 

 orbit, causing an orbital cellulitis ; (c} to the lachrymal sac (on account of the 

 contiguity of the lachrymal bone) causing dacryo-cystitis. 



A valuable, but not always reliable, sign of involvement of the ethmoidal cells, 

 is localized pain at the inner can thus of the eye (Kiimmel), and swelling of the 

 mucous membrane around the middle turbinate may in this as in infection of the 

 other sinuses be considered an important symptom. In order to evacuate the 

 diseased cells, the middle turbinate (as in the case of the sphenoidal sinus) must be 

 removed before the ethmoidal cells can be exposed. As, in the large majority of 

 cases at least, the condition is coincident with similar infection of the frontal sinus, 

 the anterior cells may be easily reached from the floor of the latter after it has been 

 opened. The optic nerve, the trochlear nerve, the superior oblique ocular muscle 

 and the anterior and posterior ethmoidal arteries, are the most important structures 

 endangered during this operation. 



DEVELOPMENT OF THE NOSE. 



The earliest trace of the nasal anlage appears about the beginning of the third 

 week of foetal life as a thickening of the ectoblast to form the nasal area at each 

 side of the anterior portion of the head. About one week later the convexly cres- 

 centic outline of this area gives place to a slight depression that deepens into the 

 olfactory pit or fossa in consequence of the increased thickness of the surrounding 

 mesoblast. The encircling ridge thus produced is best marked on the mesial and 

 lateral boundaries of the fossa (Kallius), where the resulting elevations foreshadow 

 the development of the inner and outer nasal processes. With the forward growth 

 and union of the maxillary process of the first visceral arch with the median nasal 

 process, or processus globularis, to complete the upper boundary of the primitive 

 oral cleft (page 62), the margin of the entrance of the nasal pit becomes closed in 

 below. Subsequently, however, the lateral nasal process extends medially above 

 the maxillary process until it meets the median nasal process and thus becomes the 

 immediate lower and lateral boundary of the opening of the fossa. The latter grows 

 and deepens chiefly upward, towards the brain, and backward and in consequence 

 the olfactory organ for a time consists of two blind pouches, separated by the frontal 

 process, lying above the primitive oral cavity. These pouches invade the mesoblast 

 until their blind posterior ends reach the primitive oral cavity between which and the 

 olfactory diverticula a thin partition, composed of the two abutting layers of epithe- 

 lium, alone intervenes. This septum, bucco-nasal membrane of Hochstetter, becomes 

 attenuated and finally ruptures, the resulting openings, the primitive choante, estab- 

 lishing communication between the nasal fossae and the primitive oral cavity. That 

 part of the roof of the latter which extends from the choanae to the nasal apertures 

 constitutes the primitive palate, and contributes not only the anterior portion of the 

 definite palate, but also the tissue forming the lips (Hochstetter). The primitive 

 palate includes contributions from different sources, its middle portion being from the 

 median nasal process and its lateral portions being derived from the lateral nasal 

 process in front and from the maxillary process behind (Peter). 



Subsequent to the formation of the primitive palate, about the fifth week, the 

 primitive nasal fossae increase in size, sink deeper into the head between the median 

 plane and the eye, and come into closer relation with the brain. The nasal fossae, 

 however, in acquiring their definite expansion additionally appropriate a considerable 

 portion of the primitive oral cavity which becomes separated from the remainder of 

 that space by the formation of the definite palate. 



