446 



THE RESPIBATORY APPARATUS IN MAMMALIA. 



appearance not covered by any membrane, apart from the contents of the cell, 

 which are a yellow, granular proto-plasma surrounding an oval nucleus lying 

 in colourless proto-plasma. The extremity of these cells is thin, and they 

 can be traced inwards until they expand into a flat portion that sends off pro- 

 cesses which appear to be continuous with the fibres of the submucous 

 connective tissue. Similar cells (c) are found towards the margin of the 

 true olfactory region, but these have a band at their free extremity, which is 

 also provided with a circle of cilia.) 



The pituitary membrane receives its blood by the ophthalmic and nasal 

 arteries ; it is returned by the large anastomosing veins which form, in the 

 deep layer, a long, close, and magnificent plexus that terminates in the 

 satellite vein of the nasal artery. This plexuous arrangement is so marked at 

 certain points as at the appendices of the turbinated bones, that it gives the 

 mucous membrane somewhat the appearance of erectile tissue. It will be 

 understood that in favouring the stagnation of the blood, this arrangement 

 predisposes to haemorrhage. 



The lymphatics of the pituitary membrane could not be injected for a 

 long time, neither in man nor animals ; and this led several anatomists to 

 deny their existence. Nevertheless, they do exist, and form a fine superficial 

 network on the septum of the nose, the turbinated bones, and the meatuses. 

 The trunks passing from it go to the submaxillary glands. 



The nerves of this membrane are numerous, and are derived from the 

 first and fifth pairs, and from Meckel's ganglion. The ramifications of the 

 olfactory nerve, on emerging from the apertures of the cribriform plate of 

 the ethmoid bone, pass to the inner and outer walls of the nasal cavities ; 

 being destined for the olfactory mucous membrane, they do not descend 

 below the upper third of these cavities. They form at first a close plexus, 

 and afterwards terminate in a manner not quite understood. Schultze admits 

 that they terminate on the olfactory cells mentioned above. 



The branches derived from Meckel's ganglion and the fifth pair are 

 specially destined for the Schneiderian membrane, and 

 are named the ethmoidal brandies of the palpebro-nasal 

 and spheno-palatine nerves. They endow the nose with 

 an acute degree of sensibility, and it is believed that 

 they render olf action more perfect. 



(It is to be remarked that the filaments composing 

 the olfactory plexus differ from ordinary cephalic nerves 

 in containing no white substance of Schwann, and are 

 nucleated and finely granular in texture, resembling the 

 gelatinous form of nerve-fibres. The surface to which 

 they are limited is that covered with the yellowish- 

 brown epithelium.) 



3. Sinuses. 



The sinuses are very anfractuous cavities, excavated 

 in the substance of the bones of the head, on the limits of 

 FIBRES OF ULTIMATE the cranium and face, and around the ethmoidal masses, 

 RAMIFICATIONS OF w hi c h they envelop. 



OF F Doa RY NERVE These cavities - diverticuli of the nasal fossae, are 

 pairs, and are five on each side : the frontal, super- 

 maxillary, sphenoidal, ethmoidal, and inferior maxillary sinuses. The first 

 four communicate ; the last is usually perfectly isolated. 



FRONTAL SINUS, This cavity, situated at the inner side of the orbit, 



Fig. 226. 



