94 



ANATOMY AND rHYSIOLOGY OF 



bloodvessels spread over it, which are here 

 so superficial as to owe their principal de- 

 fence to the mucous exudation : hence it 

 is that the complexion of the membrane 

 (varying with the inilucnce of the atmos- 

 phere and other agents) is extremely fugitive 

 and uncertain. The adherent surface of 

 the membrane contracts a close and firm 

 adherence to the parts it covers, through 

 the insinuation of its fibres into them : in- 

 deed, to the bone it appears to supply the 

 place of periosteum ; to the cartilage, of 

 perichondrium. The substance of the 

 membrane exhibits a fibrous structure, in- 

 terwoven with cellular tissue ; and upon 

 that — as a substratum — is spread a glan- 

 dular and vascular apparatus, from which 

 issues the mucous secretion ; together with 

 numerous papillce, of small size, constituted 

 of the terminations of those nerves from 

 which the membrane derives ordinary sen- 

 sation, as well as those that endow it with 

 the peculiar sense of smelling. The 

 Schneiderian membrane, inferiorly, within 

 the nostrils, is continuous with the duplica- 

 tures of skin lining those parts ; superiorly 

 with the membrane lining the pharynx ; be- 

 sides which, it is continued into the several 

 sinuses of the head, through the openings 

 leading from them into the nose, and like- 

 wise 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 absorbent vessels. 

 Its arteries, wliich 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-maxillary. 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 excep- 

 tion of the membrane lining them, they are 

 entirely osseous in their composition. This 

 will account for their descrijjtion having 



been already given (at page 46), to which 

 we must again refer. 



" Ducts. — There are two ducts belonging 

 to, or connected with, the nose. One is the 

 diiclus ad nasnm — a tube partly osseous 

 and partly membranous in its composition, 

 commencing at the inner angle or corner of 

 the eye, witliin the substance of the lachry- 

 mal bone, running within a canal continued 

 from this bone through the superior maxil- 

 lary 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 communis narium, 

 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." 



INTERNAL PARTS. 



COMPREHENDIXG THE CAVITIES OF THE CRANIinW, OR- 

 BIT, NOSE, AND MOUTH. 



I. CAVITY OF THE CRANIUM, 



Constructed for the lodgment of the 

 brain with its appendages, is in form ovoid, 

 flattened inferiorly, broader anteriorly than 

 posteriorly; its antero-posterior or long 

 diameter measuring about seven inches ; its 

 transverse or lateral diameter about four 

 inches ; its vertical or perpendicular diameter 

 about three and a half inches. At the same 

 time it is to be observed, that, although the 

 general form of the cavity is the same, its di- 

 mensions may and do vary in different heads. 

 The eight bones composing the cranium all 

 present internally surfaces more or less con- 

 cave, which, united, form the cavity under 

 consideration ; hence it is that the interior 

 is not regular or uniform, but presents to 

 view different hollows, which are adapted 

 to distinct prominences of the cerebral mass. 



Division of the interior surface into roof 

 and base of the cranium : 



The roof is formed by the frontal, parietal, 

 and occipital bones: its superficis is larger 



