8 



INNERVATION. 



[CHAP. xvi. 



The bulb of the olfactory process (tig. 106, b] is an elongated oval 

 mass of nervous matter, which lies upon the cribriform plate. The 

 white portions of the olfactory process terminate in its posterior ex- 

 tremity. It contains a small ventricle, which, in some of the lower 



Ficj. 106. 



\ 



Outer wall of the nasal fossa, with the three spongy bones and meatus : the nerves being shown 

 as they would appear through the membrane if it were transparent. a. Olfactory process, b. Ol- 

 factory bulb (represented rather too short) resting on the cribriform plate. Below is seen the 

 plexiform arrangement of the olfactory filaments on the upper and middle spongy bones. 

 c. Fifth nerve within the cranium with its Gas?erian ganglion, d. Its superior maxillary divi- 

 sion, sending branches to Meckel's ganglion, and through that to the three spongy bones, 

 where they anastomose with the olfactory filaments, and with s, branches of the nasal division 

 of the ophthalmic nerve, o. Posterior palatine twigs frpm Meckel's ganglion, supplying the 

 soft and hard palate, t. Orifice of the Eustachian tube on the side of the pharynx, behind 

 the lower spongy bone. From Scemmerring, two-thirds diameter. 



animals is prolonged backwards as far as the cerebral ventricles. 

 This ventricle is lined with a delicate white layer, but with this 

 exception, the whole olfactory lobe consists of gray matter. In 

 particular it is to be observed, that the under portion, which 

 reposes on the cribriform plate, and sends down the olfactory fila- 

 ments, contains no tubular fibres. 



The olfactory filaments (figs. 106, 7, 8) are from fifteen to 

 twenty-five in number, and, passing through the apertures of the cri- 

 briform plate, may be seen, invested with fibrous sheaths derived 

 from the dura mater, upon the deep or attached surface of the 

 mucous membrane of the olfactory region. They here branch, and 

 sparingly reunite in a plexiform manner, as they descend. They form 

 a considerable part of the entire thickness of the membrane, and 

 differ widely from the ordinary cerebral nerves in structure. They 

 contain no white substance of Schwann, are not divisible into 



