ORGANS OF THE BODY. 613 



i 



But the whole of this organ does not participate in the perception of 

 odours. It is only the upper portions of the two greater cavities which 

 preside over the reception of this particular kind of impressions; the 

 other parts are either accessories in the process, or merely endowed with 

 ordinary sensation through twigs of the trigeminus nerve. 



That portion of the organ designed for the perception of odours corre- 

 sponds to the distribution of the olfactory nerves. It consists generally 

 of the upper part of the septum, the superior, and portion of the middle 

 turbinated bones. It is remarkable for its yellow or brownish tint, better 

 seen in the mature than in the newly born animal, and but slightly pro- 

 nounced in man. It is further liable to vary in extent in different indi- 

 viduals, especially of the human species. To this tract the appropriate 

 name of regio olfactoria has been given (Todd and Bowman). The 

 older name of Schneiderian membrane may be retained for the remainder 

 of the mucous .surface not endowed with perceptive power. 



The bony boundaries of the organ of smell need not be described, nor 

 its cartilages, which consist of hyaline tissue. 



The external skin of the nose is thinly clothed with epidermis, and 

 contains, together with a few sweat glands, a large number of sebaceous 

 glands of considerable size ( 198). In the anterior nares strong hairs are 

 to be found, known as vibrissce, designed to prevent, to a certain extent, 

 the entrance of foreign bodies. Internally, the coating of flattened 

 epithelial cells extends for a certain distance from the entrance, and 

 then gradually gives way to a slightly laminated ciliated species already 

 alluded to, which extends from thence throughout all the cavities of the 

 organ. Here, also, we find beaker-cells, except in the regio olfactoria 

 (Schultze). 



The Schneiderian membrane, which is very vascular in the greater 

 cavities, differs much in structure in particular localities. In the acces- 

 sory cavities it is thinner, and so intimately connected with the surface 

 of the bone, that its submucous tissue plays the part of periosteum to the 

 latter. In the nasal fossae proper, the mucosa attains, on the contrary, 

 greater, and at certain points, very considerable thickness. Here it is 

 richly supplied with racemose mucous glands, which only occur very 

 sparely in the adjacent cells. It presents, also, in this region, a dense 

 plexiform arrangement of blood-vessels, especially of veins, to which 

 is due the great tendency of the nose to bleed. The mode of termina- 

 tion of the sentient nerves of the nose is still unknown. 



REMARKS. Compare Todd and. Bowman, I.e. vol. ii. p. 1, and Schultze. Unter- 

 suchungen iiber den Bau der Nasenschleimhaut, namentlich die Structur und 

 Endigungsweise der Geruchsnerven bei dem Menschen und den Wirbelthieren. 

 Halle, 1862. 



307. 



The regio olfactoria (fig. 572, left) offers for our consideration a very 

 remarkable and extremely delicate tissue, whose constituents are peculiarly 

 liable to suffer early from decomposition. For our present acquaintance 

 with its nature we are particularly indebted to ScJiultze, and before him, 

 for many points, to Eckard and Ecker. Apart from difference of colour, 

 it may be distinguished from the surrounding membrane by its greater 

 thickness, and dissimilarity in the species of glands it contains, as well as 

 in not possessing ciliated epithelium. 



The glands in question (D) have been named by Koelliker after their 

 discoverer Bowman ( 189). They belong to the tubular species, and 



