34 APPENDIX. 



laminated character. The Villosities, are semi-diaphanous, their surface is smooth, with- 

 out any appearance of a cellular or vascular texture, both of which have been impu- 

 ted to them. Professor Meckel, whilst he doubts whether or not they possess either the 

 one species of structure or the other, is inclined to believe, from analogy with certain 

 parts of some vegetables, that they consist of a continuous series of cells. 



The villosites of the mucous membrane of the intestinal canal appear to be a mode of 

 Structure which, as well as that of folds, gives an increase of the extent of surface exposed 

 to the influence of external agents. " Villosities are only more minute forms of membran- 

 ous folds, differing somewhat from the latter in the greater proportion of the extent of 

 their surface to that of their base, and thus presenting where they exist, which is 

 chiefly in the small intestines, the means by which the above-mentioned purpose may 

 be most perfectly fulfilled." 



The epidermis, or epithelium, is very manifest, at the openings into the digestive ca- 

 nal, but soon becomes much less so, as we advance into the cavities, until it becomes 

 entirely indemonstrable. The blood vessels and absorbents of this membrane are abun- 

 dant. Its nerves are chiefly of the ganglial system, but at its natural openings they come 

 also from the cerebro-spinal system. 



The functions of the mucous membrane of the digestive tube may be enumerated un- 

 der the following heads. 



1. Absorption, of which the Villosities are the most active agents, although not the 

 only agents. 



2. Secretion, which is perspiratory and follicular ; and of which the products differ- 

 ing much according to the situation whence they issue, are generally known under the 

 term mucosity. 



3. Tonic contraction, which is promoted by the action of the muscular fibres. 



4. Sensibility, varying in all its grades, and modes of manifestations. 



The mucous membrane of the intestinal canal is next to the first, if not the first of the 

 structures of the body which comes into existence. Its characters are but little modi- 

 fied by age or sex. (See the Note in the Jlppendix, on the Devclopement of the Textures 

 of the Foetus.) 



Of the Digestive process in the Intestines. It. is not necessary to say much in addition 

 to what is contained in the text. This process, as it respects the whole apparatus des- 

 tined for its performance, may be divided into three stages, namely, Chymifaction, 

 Chylifaction, and Fecation : the first is performed in the stomach, the second in the 

 small intestines, and the third in the large intestines The first has already come be- 

 fore us, and the second was noticed, when the functions of the liver were under consi- 

 deration. We may, however, remark, respecting chylifaction, that it is by no means a 

 chemical process, for there subsists no chemical relation between the chyme and the 

 biliary and pancreatic juices, which are the materials of the ne\v product ; this process 

 Is altogether a vital one, and the result is very nearly alike under every circumstance. 

 Chylifaction chiefly takes place in the duodenum and jejunum from the admixture of the 

 juices just now mentioned with the chyme. The experiments of Professor Mondini 

 confirm the inference, that the duodenum is distended with the chyme when the bile is 

 passing into it. 



The absorption of the chyle commences about the end of the duodenum, and goes on 

 throughout the jejunum, and the first half of the ilium, and is completed at the termi- 

 nation of this intestine ; this function takes place with greatest activity in the je- 

 junum. 



To the function of the larger intestines may be given the term Fecation ; because it 

 is in this situation of the digestive canal that the foccal matter is formed. In its course 

 through the small intestines the alimentary matters are deprived of their chyle, and of 

 a portion of their more aqueous parts : the residue is poured into the colon, where its 

 course is more slow and where it assumes new characters. The fecal mass, according to 

 the properties which it presents a"t the commencement of the colon is evidently composed 

 * 1st, of the residue of the aliments ; and 2d, of the excrementitial parts of the secre- 

 tions poured into the superior part of the digestive tube. The fasces, when they arrive 

 in the rectum, or at the time of their expulsion from the body, are greatly increased by 

 the more solid parts of the secretions poured out upon the internal surface of the co- 

 lon, their more fluid parts having been absorbed. It is, in some measure, owing to the 

 quantity and properties of the excrementitial parts of these latter secretions, which prin- 

 cipally proceed from the follicular apparatus of this intestine, that the fseces present 

 distinctive characters. 



Gaseous substances generally are found in greater or less abundance in the small in- 

 testines. This gas may come from more than one source : it may arise from the 

 change which the elementary substances undergo in their course ; or it may be secre- 



