DISSECTION OF THE HEAD AND NECK. 225 



connection with the nostril (page 181). It is a small opening (about the 

 same diameter as a goose quill), with a circular outline, having the appear- 

 ance as if a small circle of skin had been punched out. The opening, it 

 is to be observed, is on the skin, and not the mucous membrane, taking 

 the presence of hair as distinguishing the former from the latter. The 

 duct passes upwards beneath the mucous lining of the middle meatus 

 until it enters the osseous tube that conducts it to join the lachrymal 

 sac at the floor of the orbit. The lower portion of the tube has a 

 stratified epithelial lining, but in its upper part the epithelium is 

 ciliated. 



2. The Opening of Stenson's Canal. — Look for this opening on the 

 floor of the nasal fossa, over the incisor or naso-palatine cleft. Pass a 

 flexible probe into it. It will be found to pass obliquely into the 

 cartilaginous substance that closes this opening. It there joins another 

 canal — the organ of Jacobson, which passes upwards at the side of the 

 hinder edge of the septal cartilage, terminating blindly after a course 

 of four or five inches. The organ of Jacobson has a wall of hyaline 

 cartilage, with a mucous lining, and numerous mucous or serous 

 glands. Its epithelial lining is in part a stratified epithelium, and 

 in part it resembles the olfactory epithelium to be presently de- 

 scribed ; and to the latter portion some fibres of the olfactory nerve 

 are traceable. 



3. The Opening of Communication tvith the Sinuses of the Head. — This 

 is placed towards the upper extremity of the middle meatus. 

 Ordinarily it has the form of a curved slit not visible from the nasal 

 fossa, but if a flexible probe be insinuated between the turbinated 

 bones at this point it may be guided on into the frontal or the maxillary 

 sinus. 



The Nasal Mucous Membrane (Pituitary or Schneiderean Membrane). 

 As already seen in the examination of the nostrils, the skin is carried 

 round the edges of these, and for a short distance into the nasal fossa. 

 Along an abrupt line it loses its pigment and hair, and is continued by 

 the mucous membrane. This mucous membrane, it will be observed, 

 differs in its upper and its lower portions. Thus, in its lower three- 

 fourths the membrane has a rosy, vascular tint, while in its upper 

 fourth it is distinguished to the naked eye by being of a pale, somewhat 

 yellowish colour. The first of these may be termed the respiratory 

 portion of the membrane, as distinguished from the second, or olfactory 

 portion. The former has a stratified, columnar, ciliated epithelium 

 similar to that of the air passages in general, and in its submucous 

 tissue are numerous small racemose mucous glands. The olfactory 

 mucous membrane, on the other hand, has its free surface formed by a 

 layer of columnar cells for the most part non-ciliated ; and between the 

 bases of these are peculiar spindle-shaped olfactory cells. The olfactory 



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