CHAP. XVI.] THE OLFACTORY PROCESS OR LOBE. 7 



about -j 5*5-0 inch. We have hitherto failed in seeing any loop-like or 

 projecting capillaries in injections of adult specimens. Care must he 

 taken not to confound these loops in the olfactory region of the 

 foetus with the loops of the undoubted true papillae, situated just 

 within the nostrils, and which belong to touch. 



Of the Nerves of the Nose These are the first pair, and branches 

 of the fifth pair, besides motor filaments from the facial nerve to the 

 external muscles. The first pair has long been considered as the 

 proper nerve of smell, though not without dispute. That it has 

 been rightly so regarded, however, is evident for many reasons. Its 

 limitation to the upper and middle spongy bones, to the roof of 

 the nasal fossae, and to the upper half of the septum, where the 

 mucous membrane exhibits peculiar characters, and smell is princi- 

 pally, if not exclusively, exercised; its development in the verte- 

 brate class, proportionate, cceteris paribus, to the acuteness of smell, 

 being largest in animals of keenest scent; the loss of smell, without 

 other effect, consequent on its division; together with the perversion 

 or loss of smell found in many authentic cases in connexion with 

 disease of these nerves or their associated cerebral region : all these 

 facts point irresistibly to this conclusion. 



Of the first Pair. Under this head are to be described the 

 olfactory process or lobe, and the olfactory filaments distributed 

 to the nose. 



The olfactory process, or lobe, (a, b, fig. 106) is a slender prism 

 of fibrous and vesicular nervous matter, terminating in front in a 

 bulb; and it is sunk in the fissure which bounds the supra-orbitar 

 convolution on the under surface of the anterior lobe of the cerebrum 

 (vol. i. p. 282). It is connected with the inferior surface of the brain 

 by an external and internal root. The former is the longer, and may 

 be traced in the nervous matter forming the floor of the fissure of 

 Sylvius, and among the arteries of the locus perforatus, towards the 

 lower and outer part of the corpus striatum, near the anterior com- 

 missure of the cerebrum. In the dog and cat, where this process is 

 much larger, the anterior commissure seems to have a more intimate 

 relation to the olfactory processes. In the same animals the white 

 matter of the process is continuous also with that of the largely 

 developed hippocampus major. The internal root winds inwards, 

 and is lost in the gray matter in front of the optic commissure, near 

 the anterior extremity of the corpus callosum. In front of the point 

 where the roots join, there is a process of gray matter constituting a 

 third or gray root, and which is continued forwards as a portion of 

 the olfactory process, as far as the bulb, where it expands. 



