146 THE DISEASES AND DISORDERS OF THE OX. 



epiblast is seen in many ways. For instance, some mammals 

 develop hair within the mouth, and the majority of the members 

 of this class of animals are provided with a few hairs within the 

 nose, and also within the external auditory meatus of the ear, 

 and some also on the conjunctiva of the eye. Moreover, it is 

 well known that the Selachii show, in the clearest manner, steps 

 of transition betwixt scales on the skin on the one hand, and 

 teeth in the mouth on the other, and it is to be remarked that 

 both scales and teeth are limited to regions which have deve- 

 loped from the epiblast. Horny teeth occur in the stomachs of 

 certain animals. Again, the occurrence of hair all over the body, 

 with the exception of the palms and soles — an exception which 

 is what we should expect on account of the friction to which 

 these parts are constantly subjected — has been noted both in 

 man and in woman. 



The rashes of the specific fevers, too, sometimes illustrate the 

 similar origin of the parts which they afifect. For instance, the 

 rash of scarlet fever may occur in any part of the skin, and even 

 on the face, though its early punctate character may be rapidly 

 obscured owing to the fact that the skin of the face is naturally very 

 full of blood. The rash occurs also on the scalp, on the oral and 

 faucial mucous membranes, probably also on the nasal mucous 

 membrane as is evidenced by the constant thick stream of dis- 

 charge so frequently seen flowing from both nostrils in infants 

 and children, also on the conjunctiva, in the external auditory 

 meatus of the ear, probably also in the middle ear and Eustachian 

 tube. These latter points lead us to the recollection that the 

 mucous membranes of the fauces, Eustachian tube, middle ear, 

 and external ear are derived from the lining of one cleft — the 

 Tympano-Eustachian cleft, the representative of the permanently 

 open spiracle of the Selachii. 



Similar observations are to be made in regard to the two 

 diseases, measles and small-pox. Again, in reference to the 

 drugs, belladonna and jaborandi, we know that belladonna 

 causes dryness of all parts of the skin, including the mammary 

 involution, and also of all parts of the mouth and throat, while 

 jaborandi does the reverse of this. 



Similarly, a sufferer from rheumatic fever has a moist tongue 

 and an especially moist skin, and a phthisical patient also 

 generally has a moist tongue and skin. 



