DISSECTION OF THE HEAD AND NECK. 219 



sac at the floor of the orbit. The lower portion of the tube has a sti'ati- 

 fied 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 olfixctory epithelium to be presently described ; and to the latter 

 portion some fibres of the olfactory nerve are traceable. 



3. The Opening of Communication with 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 two turbinated bones at this 

 point, it may be guided on into the frontal or the maxillary sinus. 



The Nasal Mucous Membrane (Pituitary or Schneidercan 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 respirator?/ 

 2)ortion 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 serous or 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 cells are connected by their deep ends with the olfactory 

 nerve fibres, while their opposite extremities are insinuated between the 

 columnar cells, and terminate on the surface of the membrane in a 

 few stiff", hair-like processes. In the submucous tissue are numerous 

 tubular glands — the glands of Boivman — which open on the free surface 

 of the membrane. The nasal mucous membrane is continuous with that 

 of Stenson's canal and the organ of Jacobson, the pharynx, and the 

 sinuses of the head. 



The Olfactory (1st Cranial) Nerve. The delicate oval swelling 

 termed the olfactory bulb, whicli is lodged in the fossa of the same name 



