524 



RESPIBATORY APPARATUS IN MAMMALIA. 



Fig. 310. 



in colourless protoplasm. The extremity of these cells is thin, and they can be 

 traced inwards until they expand into a flat portion that sends off processes, 

 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 appendages 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 hemor- 

 rhage. 



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 super- 

 ficial network on the septum of the nose, the turbinated 

 bones, and the meatuses. The trunks passing from this net- 

 work 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 mem- 

 brane, and are named the ethmoidal branches 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 olfaction 

 more perfect. 



(It is to be remarked that the filaments composing the olfactory plexus, differ 

 from ordinary cranial 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.) 



FIBRES OF ULTIMATE 

 RAMIFICATIONS OF 

 OLFACTORY NERVE 

 OF DOG. 



3. The Sinuses. 



The sinuses are very winding cavities, excavated in the substance of the bones 

 of the head, on the limits of the cranium and face, and around the ethmoidal 

 masses, which they envelop. 



These cavities — diverticuli of the nasal fossae — are pairs, and are five on 

 each side, arranged in two groups: 1. The /rowto/, supermaxiUarij, sphenoidal, 

 ethmoidal sinuses. 2. The inferior maxillary sinus. The first four communicate ; 

 the last is usually perfectly isolated. 



