364 SENSITIVE SYSTEM. 



piUcCy of small size, constituted of the terminations of those nerves 

 from which the membrane derives ordinary sensation, as well as 

 those that endow it with the peculiar sense of smelling. The 

 Schneiderian membrane, inferiorly, within the nostrils, is con- 

 tinuous with the duplicatures of skin, lining those parts; supe- 

 liorly, with the membrane lining the pharynx ; besides which, it 

 is continued into the several sinuses of the head, through the 

 openings leading from them into the nose, and likewise gives 

 them a complete covering : it is to be observed, however, that in 

 the sinuses the membrane is thinner, and assumes a paler and 

 more delicate aspect; its natural secretion is also found more 

 sparing. The membrane is abundantly supplied with blood- 

 vessels, as well as nerves ; and also possesses its share of ab- 

 sorbent vessels. Its arteries, which ramify and anastomose so as 

 to form a spreading network upon the secreting surface, are 

 derived superiorly from the lateral nasal; inferiorly, from the 

 facial and palato-maxillari/. Its nerves are furnished by the 

 first and fifth pairs. 



SINUSES. These cavities are formed in the interior of 

 several of the bones of the cranium and face : in fact, with the 

 exception of the membrane lining them, they are entirely osseous 

 in their composition. This will account for their description 

 having been already given (at page 4G), to which we must again 

 refer. 



DUCTS. There are two ducts belonging to, or connected 

 with, the nose. One is the ductus ad nasum — a tube partly 

 osseous and partly membranous in its composition, connnencing 

 at the inner angle or corner of the eye, within the substance of the 

 lachrymal bone, running within a canal continued from this bone 

 through the superior maxillary bone, and terminating at the inner 

 and inferior part of the nasal fossa, underneath the duplicature 

 of the inferior ala, upon the surface of the common skin, about 

 one-fourth of an inch from its junction with the Schneiderian 

 membrane, by an orifice large enough to admit a crow-quill. 

 The other duct is the ductus comnmnis nariuni, which pursues 

 its course along underneath the vomer to the pharynx ; after 

 arising from two lateral branches springing from oblong apertures 

 in the floor of the nostrils. 



OF THE EYE. 



The parts comprehended under this organ of sense are com- 

 monly divided into tlwie immediately concerned i)i the production 

 of vision, and those that are Out auxiliarj/ to the function : in 

 other words, into the Eyeball and its Ai'PENDAGiis. 



