392 . NERVOUS SYSTEM. 



part of the inferior spongy bone, this membrane is continued 

 into the lining membrane of the lachrymal sac, and there forms 

 a fold, frequently resembling a valve. Along the posterior mar- 

 gin of the vomer, the membrane of the nostril is continued into 

 the corresponding one of the other side, whose arrangement is 

 in all respects the same. 



The pituitary membrane, in its structure and appearance, re- 

 sembles other mucous membranes; its colour, however, is na- 

 turally of a deeper red. It Consists of two laminse, which can- 

 not be readily separated: the one next to the cavity of the nos- 

 tril has the mucous structure ; the exterior one is fibrous, and 

 resembles the periosteum of other parts of the body. This 

 composition is best seen on the part belonging to the septum 

 narium. 



By floating the pituitary membrane in water its mucous la- 

 mina is made to exhibit, very satisfactorily, the villous and 

 spongy appearance. This is particularly evident on the turbi- 

 nated bones. Its whole surface is studded with pits or folli- 

 cles of various sizes, irregularly arranged and resembling pricks 

 made into a plastic substance with the point of a pin. From 

 these cavities or cryptse proceeds the mucus of the nose. In the 

 thickness of the pituitary membrane, there exist numerous and 

 thickly set glands, of a size so small that they escape common 

 observation, but their existence is generally admitted, both on 

 the authority of anatomists who have described them,* and on 

 the principle of their being always the concomitants of mucous 

 membranes"! 



It is owing to the great abundance of blood vessels in this 

 membrane, to their very superficial course, and to the habitual 

 residence of blood in them, that it always presents a deep red 

 colour in the living state. These blood vessels bleed very 

 freely from slight mechanical causes, and are also disposed to 

 congestions, which are relieved by the blood being poured out 

 through their exhalent orifices, without laceration or any solu- 

 tion of continuity. 



Though the description just given corresponds with the tex- 

 ture, generally, of the pituitary membrane, yet there are modi- 

 fications of the latter at particular points which it does not fully 



* Ruyschii, Epist. Anat. Probl. vii. Mayer. t Biehat, Ariat. Descriji. 



