406 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



The lymphatics constitute three superposed networks in the nracous 

 membrane. The first is situated around the glandular orifices ; it receives 



Fig. 202. 



HORIZONTAL SECTION THROUGH THE MIDDLE PLANE OP THREE PETERIAN GLANDS, 

 SHOWING THE DISTRIBUTION OF THE BLOOD-VESSELS IN THEIR INTEBIOR. 



the central lacteal from 



Fig. 203 



DIAGRAMMATIC REPRESENTA- 

 TION OF THE ORIGIN OF 

 THE LACTEALS IN A VILLUS. 



e, Central lacteal ; d, Connec- 

 tive-tissue corpuscles with 

 communicating branches ; 

 c, Ciliated columnar epithe- 

 lial cells, the attached ex- 

 tremities of which are di- 

 rectly contiguous with -the 

 connective tissue corpuscles. 



each villus; the second is placed between the 

 glandular and the muscular layer of the mucous 

 membrane ; finally, the third exists in the deep 

 portion of the membrane, and communicates with 

 the meshes encircling the closed follicles. The 

 most voluminous emergent vessels pass through 

 the wall of the intestine and accompany the blood- 

 vessels between the layers of the mesentery, enter- 

 ing the mesenteric glands, and terminating in the 

 reservoir of Pecquet (receptaculum chyli). 



The nerves are from the solar plexus; they 

 form a submucous reticulation and a myenteric 

 plexus, comprised between the two planes of the 

 muscular tunic. 



Microscopic ganglia are found on their course. 



Development. — The small intestine shows it- 

 self at an early period in the foetus, and during 

 the foetal existence of Euminants preserves a very 

 remarkable predominance over the large intestine : 

 a predominance equally marked in the vessels it 

 receives, for, in a fcetus of five months, we have 

 found the collective arteries of the small intes- 

 tine equivalent to about ten times the volume of 

 those of the caecum and colon. 



Functions. — It is in this tube, and under the 



