THE ABDOMEN 803 



The mesogastrium (part of the primitive dorsal mesentery), as stated, gives 

 rise to — (i ) the great or gastro-colic omentum ; {2) the gastro-splenic omentum ; 

 and (3) the heno-renal ligament. 



2 . Mesoduo-ienum. — This fold disappears, so that the duodenum, except for 

 about an inch at its commencement, is retroperitoneal. 



3. Meso jejunum and Meso-ileum. — These folds persist and constitute the 

 mesentery proper. Its dorsal end contains the superior mesenteric artery, 

 and is of hmited extent. As the jejunum and ileum increase in length, the 

 intestinal end of the mesentery prop>er acquires a much greater length than 

 the vertebral end. Moreover, as these parts of the intestinal tube become 

 coiled, the mesentery- proper towards its intestinal end becomes curv'ed, and 

 presents a number of segments of circles, which impart to it an undulating 

 outline. 



4. Caecum. — The csecum, being originally a bud or outgrowth of the gut, 

 has no mesentery, and is entirely surrounded by peritoneum. 



5. Vermiform Appendix. — The vermiform appendix, being originaUj- the 

 bhud narrowed end of the caecum, or, in other words, a diverticulum of the 

 caecum, is also destitute of a mesentery, properly so called, and is invested by 

 an extension of the peritoneal envelope of the caecum. There is, however, in 

 most cases a fold of peritoneum pertaining to the vermiform appendix, which 

 extends along it for about | or § of its length. This fold is called the meso- 

 appendlx or appendicular mesentery, and it is derived from the left or inferior 

 layer of the mesenten.- proper, close to the ileo-cohc junction. 



6. Ascending Mesocolon. — This fold, in most cases, disappears. 



7. Transverse Mesocolon. — This fold is persistent. 



8. Descending Mesocolon. — ^This fold, hke the ascending mesocolon, in most 

 cases disappears. 



9. Iliac Mesocolon. — This fold in most cases disappears. 



10. Pelvic Mesocolon. — This fold is persistent. 

 Ti. Mesorectum. — This fold disappears. 



Structure of the Liver. 



The liver has two coats, external and internal. The external or 

 serous coat is formed by the peritoneum, and is incomplete (see 

 p. 708). Within the serous coat is the fibrous or areolar coat, 

 which is kno^vn as the fibrous capsule of the organ. It is for the 

 most part thin, except where the peritoneal coat is deficient. It 

 is continuous all over the surface with the scanty amoimt of areolar 

 tissue which pervades the interior of the organ and connects the 

 hepatic lobules. At the portal fissure it surrounds the hepatic 

 duct, hepatic artery, and vena portae, under the name of the capsule 

 of Glisson. The subdivisions of this capsule accompany the various 

 branches of the duct, artery, and vein as these ramify throughout 

 the liver in the portal canals. The liver-substance is composed of a 

 great number of small polyhedral masses, called hepatic lobules, 

 which are closely packed together, and are set, each by one surface, 

 on the walls of the sublobular veins, to which they are attached 

 by means of intralobular or central veins. In man there is 

 very little areolar tissue between the lobules, which are therefore 

 for the most part confluent. In some animals, however, notably 

 the pig and camel, there is a very distinct amount of areolar tissue 

 between the lobules, which, therefore, stand clearly apart from each 

 -Other. 



