OF THE TEGUMENTARY MEMBRANES IN GENERAL. 189 



tween the teguments and the mass of the body, and vice versa; 

 a relation which is daily rendered obvious by observation, one 

 which morbid causes are continually putting in action, from 

 the observation of whose symptoms the practitioner endea- 

 vours to profit. 



256. We have already stated that the embryo is wholly 

 formed on these membranes: the vitellar or intestinal mem- 

 brane is the first that appears in the egg; it is by its prolonga- 

 tion towards the stomach, and towards the anus that the intes- 

 tine is formed. The second apparent part is the allantoid or 

 the vesical membrane, by the extension of which the urinary 

 passages and genital organs are formed. The external skin is 

 next produced: at first widely open in front of the trunk, it 

 closes in the median line of the abdomen, and finallj T , round 

 the umbilicus. In the two sexes there is a great difference of 

 conformation in the genito-urinary portion of the teguments, 

 and a difference of development in that of the excretory ducts 

 of the mammae. Besides this, there is a difference of colour- 

 ing and of thickness in the external skin. These differences 

 are well marked in the various races of the human species, and 

 are also visible in individuals. 



257. Morbid changes are very numerous in the different 

 parts of the tegumentary membrane. Accidental, cutaneous, 

 and mucous productions frequently occur. Reproductions of 

 the tegument or cicatrices, are seen daily. Vices of conforma- 

 tion, alterations of texture and functions, accidental produc- 

 tions, analogous or not to the healthy tissue, transformations 

 of tissue, &c. are also frequently observable in the teguments; 

 but their description will be better placed after that of each of 

 these membranes; the same observation will apply to their 

 cadaverous alterations. 



258. The accidental teguments, on the contrary, should 

 be described here, because, on the one hand, their production 

 is very analogous in both teguments; and on the other, because 

 in the production of an external cicatrix, the new tissue, during 

 one period of its formation, resembles the mucous membrane, 

 and at a later one, the skin; and finally, because in some cases 

 we find the appearance and texture of the skin in one part, and 



