SENSE OF SMELL. 



605 



Fig. 188. 



malia has a brownish tinge; 2dly, in its softer and more succulent 

 consistenc} 7 ^ ; and 3dly, in the greater thickness, not only of the whole 

 membrane but also of its epithelial layer. According to Kolliker, the 

 epithelium of the olfactory membrane, in the sheep and the rabbit, is 

 from 60 to 66 per cent, thicker than that of the remaining nasal mucous 

 membrane. It also differs, according to the same observer, in the 

 character of its surface. In most of the quadrupeds the epithelium of 

 the Schneiderian mucous membrane generally is covered with vibrating 

 cilia, which are absent in the olfactory portion ; though in man the vibrat- 

 ing cilia may also be found in the epithelium of the olfactory portion 

 itself. This difference of structure is probably connected with the 

 inferior acuteness of the sense of smell in man, as compared with many 

 of the lower animals. 



The nasal passages are provided with nerves from three different 

 sources. 



I. The first and most important of these are the filaments of the 

 olfactory nerve (Fig. 188, i). They are derived immediately from the 

 olfactory bulb, which rests upon the cribriform plate of the ethmoid 

 bone, and from which they penetrate the nasal passages through the 

 perforations in this bony 

 lamina. An important pecu- 

 liarity, however, shows itself 

 in the nerve fibres of this 

 region. While the substance 

 of the so-called olfactory 

 nerves within the cranial 

 cavity, as well as that of the 

 olfactory bulb, contains dark 

 bordered medullated nerve 

 fibres, like those in other 

 parts of the white substance 

 of the brain, the filaments 

 which are given off from the 

 under side of the olfactory 

 bulb, and are distributed to 

 the Olfactory membrane, Con- DISTRIBUTION OF NEBVES i* THE NASAL 

 tain Only pale, flattened, PASSAGES. 1. Olfactory bulb, with its nerves. 2. 



nucleated nerve-fibres with- ^JiT 11 f the fifth pair< 3< s P hen -P alatine 

 out a medullary layer. The 



main question of interest in regard to them is that of their final mode 

 of termination; but this, as in so many other similar cases, has thus far 

 escaped absolute demonstration. The branches of the olfactory nerves 

 frequently divide and subdivide, forming microscopic plexuses in the 

 substance of the olfactory membrane ; and the finest nervous ramifica- 

 tions are to be followed without doubt nearly to the epithelial surface 

 f the membrane itself. According to the researches of Schultze, con- 

 firmed by these of Kolliker and Babuchin, the epitheMum of this part 



