LYMPHATIC SYSTEM. 187 



The present Professor Monro has distinguished himself in this 

 subject; from his observations 1 and those of Dr. Hunter, 2 the 

 notion of the lymphatics being continued from arteries seems 

 to be very fairly exploded. And it is made probable that the 

 injections in dead bodies had misled their predecessors, who 

 had not been sufficiently aware that these injections might 

 possibly have passed, not by natural, but by forced passages. 



CHAPTER XII. 



ON THE STRUCTURE OF THE VILLI OF THE INTESTINES, AND THE 

 MANNED IN WHICH ABSORPTION IS PERFORMED. 



THE term villi, applied to the very small processes of the in- 

 ternal coat of the intestines, conveys an improper idea of their 

 figure in the human body. In many quadrupeds indeed they 

 are cylindrical, or like hairs or wool ; 3 but in the human sub- 

 ject they are broad and flat ; and when viewed with a microscope 



1 De Ven. Lymph. Valv. 2 Medical Commentaries. 



3 I have seen them of that shape in the dog, cat, lion, and the ass (LXXXV *). 



(LXXXV*.) Of the intestinal villi, Professor Miiller* observes, " It 

 is true that they are flattened in most mammalia, as in the rabbit, dog, 

 and hog ; but in the calf, ox, and sheep, many of the villi are cylin- 

 drical ; and sometimes, as in the sheep and ox, the flattened villi are 

 more numerous in one part of the intestines, in another part the cylin- 

 drical ; and in the two last-named animals, particularly in the sheep, 

 the villi in many parts of the intestines are flattened and broad, with 

 cylindrical tips. By the villi becoming broader at their base, and be- 

 ing connected with each other so as to form folds, a gradual transition 

 is established from the villi of mammalia to the rugae or folds by which 

 they are replaced in many birds and in reptiles. This transition is some- 

 times perceptible in the intestines of one and the same animal." He 

 adds, that the villi, especially those of the cylindrical form, contain a 

 simple cavity, which he has observed in the calf and ox ; and, with the 

 assistance of a microscopic examination by Henle, in the human sub- 

 ject. Professor Wagner b made the interesting observation that the villi 

 in the human small intestine differ in shape at different periods of life. 



a Physiology, tr. by Dr. Baly, 1st edit. b Physiology, tr. by Dr. Willis, pp. 323-4. 

 pp. 267-8. 



