438 



ANATOMY OF VERTEBRATES. 



338 



about 20 feet in length and 1^ inches in diameter. 1 Its beginning, 

 fig. 335, f, curves outward and backward to the under surface of 

 the right lobe of the liver, and has an entire investment of 

 peritoneum : the gut descends along the inner border of the 

 right kidney, where the posterior wall is left uncovered by the 

 peritoneum, and is attached by cellular tissue to the subjacent 

 parts : it then crosses below the pancreas, be- 

 hind the stomach, to the left, having a partial 

 covering of peritoneum, and only regains 

 the entire serous coat where it emerges to 

 form the beginning of the next part of the 

 small intestine. This is termed c jejunum,' 

 fig. 332, j, from its usual emptiness, and the 

 rest of the tube is ' ileum,' ib. I : these con- 

 volutions are suspended upon the duplica- 

 ture of peritoneum called e mesentery.' The 

 muscular tunic of the intestine consists of an 

 outer longitudinal and an inner transverse or 

 circular stratum; both layers being some- 

 what stronger in the duodenum. The mu- 

 cous membrane begins, in the second portion 

 miventes,' Human f the duodenum, to be disposed in transverse 

 folds called by the old Anthropotomists 

 1 valvulge conniventes,' fig. 338, as tending to impede, while, at the 

 339 same time, conniving at, the passage of 



the chyme; but, in truth, extending the 

 surface to which the chyme adheres in 

 the process of elimination of the chyle : 

 their direction at right angles to the 

 course of peristalsis not only checks 

 the passage but insures the admixture 

 of the various constituents of the chyme. 

 The alterative and absorbent surface 

 of the small intestine is further aug- 

 mented, as in most Mammals, by the 

 minute filamentary processes which, 

 giving the free surface a velvety cha- 

 racter, are termed ( villi.' In the mag- 

 nified section of the intestinal tunics, 

 fig. 339, a are the villi, c the submu- 

 cous areolar tissue, e transverse fibres, / longitudinal fibres of the 



1 The length of the body from the vertex to the vent, not to the heel, is that which 

 should be taken for comparison of proportionate length of the intestines in Man with 

 those of brutes recorded in the ' Tables ' of xn, tome iv. pp. 182-208. 



Valvulae com 

 small intestine, cxlviii' 



"Ml^^yMm 



Section of Human jejunum : magn. 50 

 diam. cxlviii". 



