villiform ones in the intestinal mucous membrane of some animals (vol. ii. p. 170), and subdividing, as in those, into the villi' or papillæ truly answerable to those of the skin; the tonguepapillæ or processes differ, therefore, from the true dermal papillæ in standing freely out from the surface of the epithelium, which is moulded upon them, and does not plaster them over to its own level. The so-called lingual papillæ are of three kinds, fossulate' or circumvallate, fungiform,' and conical,' many of the latter being also called 'filiform.'

The fossulate papilla, fig. 148, a, is large, obtuse, subpedun

148

culate, and arises from a fossa, b, by the thickened and often crenate borders of which, c, it is surrounded. The nerves and vessels enter the papilla at its pedicle; and the expanded summit subdivides into the secondary true papillæ, plastered over by the epithelium. The average number of fossulate papillæ in Man is eight, arranged as in fig. 141, f: there be sometimes ten, rarely more; often fewer than eight, but not less than four. Their arrangement may vary to that of an almost transverse line. They are supplied by branches of the glossopharyngeal; are very vascular; and, from the thinness of the epithelium, appear red when injected.

The fungiform papillæ,' fig. 149, B, are subpedunculate, but

smaller than the fossulate and rounder: they are scattered over the sides and tip of the tongue, and on the dorsum anterior to the fossulate series. They are rather larger than the filiform, and conspicuous by their red colour. They are covered by

secondary papillæ, ib. A, in which the capillaries diverge and divide to form their brush of loops, as in fig. 149, B, receiving each its capillary loop, into the fasciculus of which the branch of the artery a and vein v subdivides on entering the mushroom-like papilla or process.

The conical papillæ clothe as in a close-set pile the anterior two-thirds of the dorsum: they are longest at the mid-line near the centre of the tongue, smallest near the sides and at the tip. The cone-form, with secondary papillæ down its sides, fig. 150, merges into the cylindrical form, fig.

151, with a terminal brush of filaments.

150

The excess of the scaly

6

covering of these, ib. a, b, c, forms the so-called fur' of the

tongue, which becomes separated

from the deeper layer of epithe

151

lium, d. In the conical variety, fig. 150, a is the basal membrane, b, c, the 'processes,' subdividing into secondary or true papillæ, e, the deep layer of epithelium, f, the superficial layer, h, the points from which the filamentary prolongations would have projected: these sometimes resemble fine hairs. The function of such filiform papillæ appears to be 'portative" and protective,' that of the conical papillæ mainly tactile,' that of the fungiform and fossulate ones gustative:' behind the latter are the principal mucous follicles.

The so-called gustatory branch of the fifth supplies the fungi

a

d

Filiform papillæ. CCXL.

form, conical, and filiform papilla; the glossopharyngeal serves

the fossulate papillæ and the mucous tract behind: the ninth or hypoglossal is expended upon the muscular tissue.

§ 215. Organ of Smell.-Most Mammals are remarkable for the degree in which the sense of smell is serviceable. The class is characterised by the extent of the pituitary surface and the size and number of the olfactory nerves; nevertheless, both extremes are therein exemplified, although the family (Delphinida) in which the organ is wanting is exceptional and maximised development the rule.

The progress is not, as with the organ of taste, pari passu with the rise in the class: both Man and monkeys are below most quadrupeds in olfactory endowments. In hoofed ones smell is important in the the discrimination of wholesome from noxious food: taste would be a tedious test, the sapid matter needing to be moved about or masticated, mixed with fluid, and more or less dissolved, before the tongue can exert its gustative power; but 'smell is done at once.'' Most flesh-feeders scent afar their food.

In Mammals, as in all air-breathers, the odorous atoms strike upon the olfactory membrane at the entry of the breathing passages, where the atmosphere is filtered, as it were, through the organ of smell before reaching the windpipe; and most effectively and instructively in the pinnigrade Carnivora.

The olfactory organ in Mammals receives its special endowment from nerves which rise in numbers from their proper encephalic centre, fig. 46, 47, R. They pass out by as many holes in the plate of the prefrontal, which is thence called the cribriform,' or, from the Greek-root, ethmoid:' but the sieve-like structure is a strictly mammalian peculiarity consequent on the multiplicity of olfactory nerves, and is only affected by a single exception in this class, the Ornithorhynchus adhering to the wider Vertebrate rule.

The nerves carry out with them, each an investment of the brain-membranes; the dura mater losing itself in the periosteum, the pia mater in neurilemma, the arachnoid being reflected back. The nerves are grouped in all Mammals into a set for the septum, and a second for the upper or ethmo-turbinals, a third or middle short set being, in some, distinguishable for the labyrinth or roof of the nasal chamber. The branches of the second set, after expanding on the ethmo-turbinal, usually converge to become connected with the lateral nasal branch of the fifth.' Their mode of distribution is best seen on the ethmo-turbinal:

1 xx. vol. iii. p. 86.

here they divide, subside, expand, and anastomose with each other, forming a reticulate nervous expanse, with long and narrow meshes, and becoming impacted in the central or inner layer of the olfactive membrane. This membrane is continued into the pituitary one, covering the inferior spongy bone or 'maxillo-turbinal' supplied mainly by the fifth. Both tracts, and especially the latter, are richly supplied with arteries opening into numerous large plexiform veins on the peripheral side of the membrane, occasioning or resembling, there, a cavernous structure, and admitting of such change in the quantity of blood therein as must be attended with concomitant degrees of laxity or tension of the scenting membrane itself. This at the attachment of the turbinals is continuous with the lining of the nasal chamber; which itself becomes modified into the more delicate and still less vascular membrane of the contiguous or accessory air-sinuses. The nasal membranes are finally continued at the posterior aperture into the mucous membrane of the fauces and pharynx, and at the anterior one into the integuments of the face. The pigmental layer of the skin is soon lost within the nose, the colour of the pituitary and olfactory membranes being due to the abundant blood sent to them. Numerous mucous crypts are imbedded in the pituitary part of the nasal membrane.

The cavity containing the organ of smell is formed by the prefrontal, vomerine, nasal, sphenoid, pterygoid, palatine, maxillary, and premaxillary bones, and may be continued by extension of air-sinuses into all the bones of the cranium, figs. 154 and 157. The cavity is divided by a medial partition of bone and gristle in varying proportions, the bone being contributed by the prefrontals, the vomer, and by ridges of the nasals, palatines, maxillaries, and premaxillaries, with which the vomer may articulate. Each half of the cavity is a passage for the respiratory currents of air, opening anteriorly upon a more or less produced and mobile part called nose,'' snout,' or 'proboscis,' and posteriorly into a cavity containing the larynx or beginning of the windpipe; sometimes, as in Cetacea and in Marsupials at their mammary stage, containing the larynx exclusively, but commonly communicating also with more or less of the pharynx. In the section of the human skull, fig. 152, the outer wall of the right nasal passage is shown, with the communicating frontal, 3, and sphenoidal, 4, sinuses; 1 is the nasal bone, and a the nasal spine

1 LXXXII. p 278, and LIV. p. 128. (The second edition of this valuable and original work, 4to, 1864, is the one cited in the present volume.)

of the frontal, forming the fore part of the roof, c, the basisphenoid, forming its back part; the cribriform plate and spine' of the prefrontal completing the roof: b is the nasal plate of the maxillary bounding laterally the anterior aperture; d, pterygoid, similarly bounding the posterior aperture: the floor of the passage is formed by the premaxillary, 7, the maxillary, k, and the palatine, 6. At the upper part of the outer wall is a thin quadrilateral

152

part of the prefrontal sculptured by grooves and apertures for the olfactory nerves; the posterior part, f, is a little curved, and leaves a space into which the sphenoidal sinus opens. The convolute, thin, reticulate, bony, and gristly lamina, called 'superior turbinal,' is here attached, below which is the division of the general passage, called 'superior meatus.' This is bounded below by a similar longer and larger turbinal,' called middle spongy bone' in Anthropo

View of the outer wall of the nasal cavity on the right tomy, but usually less dis

side.

tinct from the upper part of

the ethmo-turbinal' in lower Mammals. The part of the passage between the middle and lower turbinal is the middle meatus,' into which the antrum' or maxillary sinus opens. The lower turbinal is the largest of the three, and longest retains its individuality below it is the inferior meatus,' k, into which the lacrymal canal opens.

In most lower Mammals there is a turbinal process from the frontal and nasal bones; which, from its relative position in their horizontally elongated nasal chamber, is called the 'superior spongy bone' (oberste muschel, Gurlt), by Hippotomists; it is not the homologue of that so called in Anthropotomy.

At the floor of the lower meatus, close to the premaxillomaxillary ridge supporting the fore part of the septum, is a depression or groove lined by a glandular tract of the pituitary membrane which, in Ungulates, is extended upon a long and narrow gristly sheath at that part, and communicates with the palate by the foramen incisivum. From one to three of the septal branches of the olfactory, traceable from a yellowish grey