SMELL. 



699 



ance throughout ; except that, in many in- 

 stances, a layer of those lying deepest, or 

 almost deepest, is of a darker colour than the 

 rest, from the brown pigment contained in 

 the cells. These epithelial particles, then, 

 are not ciliated ; and they form a thick, soft, 

 and pulpy stratum, resting on the basement 

 membrane. The deepest layer often adheres 

 after the others are washed away." The 

 vessels of the olfactive membrane in the 

 foetus present a regular series of papillary 

 loops ; but these cannot be seen in the adult. 

 " The olfactory filaments 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 

 elementary fibrillee, are nucleated and finely 

 granular in texture, and are invested with a 

 sheath of homogenous membrane." These 

 nerves thus rather correspond with the gela- 

 tinous fibres, than with the ordinary tubular 

 fibres of the trunks and branches of true 

 nerves ; and they are regarded by the authors 

 as direct continuations of the vesicular matter 

 of the olfactory bulb or ganglion. " Although 

 these nucleated olfactory filaments lie in 

 great abundance under the mucous membrane 

 of the olfactory region, we have been quite 

 foiled in our attempts to trace their ultimate 

 distribution in the membrane, and the diffi- 

 culty is attributable to their want of the 

 characteristic white substance. Their elon- 

 gated nuclei render the larger branches un- 

 mistakeable ; but if these become resolved at 

 last into fibrous elements, the nuclei cease to 

 be distinct from those of the numerous nu- 

 cleated tissues which they traverse." " We 

 are averse from speculating prematurely on 

 the meaning of anatomical facts ; but as some 

 hypothesis will intrude itself, we would ven- 

 ture to hint that the amalgamation of the 

 elements of the peripheral part of the nervous 

 apparatus in the larger branches, and probably 

 in the most remote distribution, as well as 

 the nucleated character indicative of an 

 essential continuity of tissue with the vesi- 

 cular matter of the lobe, are in accordance 

 with the oneness of the sensation resulting 

 from simultaneous impressions on different 

 parts of this organ of sense, and seem to 

 show that it would be most correct to speak 

 of the first pair of nerves as a portion of the 

 nervous centre put forward beyond the cra- 

 nium, in order that it may there receive, 

 as at first hand, the impressions of which 

 the mind is to become cognisant."* It 

 has also been remarked by the same excel- 

 lent observers f , that on the septum narium 

 and spongy bones bounding the direct pas- 

 sage from the nostrils to the throat, the 

 lining membrane is rendered thick and spongy 

 by the presence of ample and capacious sub- 

 mucous plexus of both arteries and veins, of 

 which the latter are by far the larger and 



* Physiological Anatomy and Physiology of 

 vol. ii. pp. 5 11. 

 f Oj>. cit. p. o. 



more tortuous. And they surmise, with 

 much probability, that the chief use of these 

 may be to impart warmth to the air, before it 

 enters the proper olfactive portion of the 

 cavity ; as well as to afford a copious supply 

 of moisture, which may be exhaled by the 

 abundant glanduke seated in the membrane;. 

 " The remarkable complexity of the lower 

 turbinated bones in animals with active scent, 

 without any ascertained distribution of the 

 olfactory nerves upon them, has given coun- 

 tenance to the supposition that the fifth nerve 

 may possess some olfactory endowment, and 

 seems not to have been explained by those 

 who rejected that idea. If considered as 

 accessory to the perfection of the sense in 

 the way above alluded to, this striking 

 arrangement will be found consistent witli 

 the view which thus limits the power of 

 smell to the first pair of nerves." * 



The olfactive organ, in other air-breathing 

 Vertebrata, corresponds with that of man in 

 all the essential particulars of its structure ; 

 being a cavity opening anteriorly upon the 

 face by the external or anterior nares, and 

 posteriorly into the upper part of the pharynx 

 by the internal or posterior nares. It may thus 

 be considered as the entrance of the respi- 

 ratory passages, which is dilated for the ex- 

 tension of the olfactive membrane ; or, per- 

 haps, it would be more correct to speak of it 

 as a diverticulum from the commencement of 

 the respiratory tube, since, as we have seen, 

 the proper olfactive organ does not extend 

 into that portion of the cavity which is placed 

 in a direct line between the anterior and pos- 

 terior nares. The development of the olfac- 

 tive organ, as measured by the size of the 

 olfactory ganglia and nerves, and by the ex- 

 tent of the surface over which these are dis- 

 tributed, varies greatly in different tribes ; and 

 details must be sought on this subject under 

 the respective names of the classes and orders 

 of vertebrata. The chief departure from the 

 ordinary type is observable in the case of the 

 Cetacea, in which the nasal cavity is almost 

 entirely devoted to the purposes of respiration, 

 and to the ejection of the water taken in by 

 the mouth with the food. To animals which 

 seek their prey in the water, an organ of 

 smell, adapted to take cognisance of odorous 

 emanations contained in the inspired air, 

 would obviously be entirely useless ; and it is 

 probable that whatever olfactive power they 

 possess is called into exercise by the passage 

 of the water that is spouted through the nos- 

 tril. The ordinary statement that the Cetacea 

 are entirely destitute of olfactive ganglia ami 

 nerves, and that they must therefore be en- 

 tirely devoid of the sense of smell, is true 

 only of the Dclplnmdtc, or that division of 

 the order which includes the dolphins and 

 porpoises ; for the Baltcnlda;, or proper 

 whales, do possess olfactive nerves, although 

 these are comparatively of small size; and in 

 the Manatidce, or herbivorous whales, which 

 properly belong rather to the Pachydermata 



* Op. cit. p. 12. 



