PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 263 



The nuclei of the muscular fibres of the villi may be shown by treating them with 

 acetic acid after the epithelium has been removed. These fibres appear to be longi- 

 tudinal, forming a thin layer surrounding the villus, about half-way between the pe- 

 riphery and the centre and continuous with the muscular coat of the intestine. The mus- 

 cular fibres, from their arrangement, would seem to be capable of shortening the villus ; 

 and this has actually been observed in specimens taken from the intestine shortly after 

 death. 



The anatomy of the lacteals as they originate in the villi has been the subject of much 

 controversy ; but almost all anatomists are now agreed that these vessels commence by 

 blind extremities, which are either single or present a few short, rounded cliverticula 

 leading to a single tube. 



Owing to the excessive tenuity of the walls of the lacteals in the villi, it has been 

 found impossible to fill them with an artificial injection, although the lymphatics sub- 

 jacent to them may be easily distended and studied in this way. Those who profess to 

 have seen the single lacteal in the villus have done so by examining the parts when the 

 lacteal system has been engorged with chyle. 



We must still regard the question of the origin of the lacteals in the intestinal villi as 

 one of great obscurity. They may originate by a delicate, anastomosing plexus, just be- 

 neath the epithelium, as is thought probable by Sappey, or the chyle may pass through 

 the epithelial layer and a part of the substance of the villus, according to the view pre- 

 sented by Eecklinghausen, without the intervention of distinct vessels, until the particles 

 reach the central tube. 



No satisfactory account has ever been given of nerves in the intestinal villi. If any 

 exist in these structures, they probably are derived from the sympathetic system, which 

 is largely distributed to the intestinal canal. 



The solitary glands or follicles and the patches of Peyer, or agminated glands, have 

 one and the same structure, the only difference being that those called solitary are scat- 

 tered singly in very variable numbers throughout the small and large intestine, while the 

 agminated glands consist of numbers of these follicles collected into patches of different 

 sizes. These patches are generally found in the ileum. The number of the solitary 

 glands is so variable that it is impossible to give any general estimate of it. They are 

 sometimes absent. The patches of Peyer are always situated in that portion of the intes- 

 tine opposite the attachment of the mesentery. They are likewise variable in number 

 and are irregular in size. They usually are irregularly-oval in form, and measure from 

 half an inch to an inch and a half in length by three-fourths of an inch in breadth. 

 Sometimes they are three or four inches long, but the largest are always found in 

 the lower part of the ileum. Their number is about twenty, and they are generally 

 confined to the ileum ; but when they are very numerous for they sometimes exist 

 to the number of sixty or eighty they may be found in the jejunum or even in the 

 duodenum. 



Two varieties of the patches of Peyer have been lately described by anatomists. In 

 one of these varieties, the patch is quite prominent, its surface being slightly raised 

 above the general mucous surface, while, in the other, the surface is smooth, and the 

 patch is distinguished at first with some difficulty. The more prominent patches are cov- 

 ered with mucous membrane arranged in folds something like the convolutions on the 

 surface of the brain. The valvular conniventes are arrested at or very near their borders. 

 These are the only patches which are generally described as the glands of Peyer, the 

 others, which may be called the smooth patches, being generally overlooked. The latter 

 are covered with a smooth, thin, and closely-adherent mucous membrane. Their follicles 

 are small and numerous. The borders of these patches are much less strongly marked than 

 those of the first variety. As they are evident only upon close examination and as they 

 are the only patches present in certain individuals, it is said that sometimes the patches 

 of Peyer are entirely w an ting. They are generally less numerous than the first variety 



