96 iv. 3 — iv. 4. 



filtered in, it will be concocted by the heat of the part, and will 

 be converted into suet or lard, and will not acquire a flesh-like or 

 sanguineous constitution. The development, then, of the omentum 

 is simply the result of necessity. But when once formed, it is 

 used by nature for an end, namely, to facilitate and to hasten the 

 concoction of food.^ For all that is hot aids concoction ; and fat 

 is hot, and the omentum is fat. .This too explains why it hangs 

 from the middle of the stomach ; for the upper part of the stomach 

 has no need of it, being assisted in concoction by the neighbouring 

 liver. Thus much as concerns the omentum. 



(Ch. 4.) The so-called mesentery is also a membrane ; and 

 stretches from the intestines, in their whole extent, to the great 

 vessel and the aorta. In it are numerous and close-packed vessels, 

 which run from the intestines into the great vessel and into the 

 aorta. The formation of this mertibrane we shall find to be the 

 result of necessity, as is that of the other parts.^ What however 

 is the final cause of its existence in sanguineous animals is 

 manifest on reflection. For it is necessary that animals shall 

 get nutriment from without ; and, again, that this shall be con- 

 verted into the ultimate nutriment, which is then distributed as 

 sustenance to the various parts ; this ultimate nutriment being, 

 in sanguineous animals, what we caJl blood, and having, in ex- 

 sanguineous animals, no definite name. . This being so, there 

 must be channels through which the nutriment shall pass, as it 

 were through roots,^ from the stomach into the blood-vessels. 

 Now the roots of plants are in the ground ; for thence their 

 nutriment is derived. But in animals the stomach and intestines 

 represent the ground, from which the nutriment is to be taken. 

 The mesentery, then, is an organ to contain the roots ; and these 

 rpots are the vessels that traverse it. This then is the final 

 cause of its existence. But how it absorbs nutriment, and how 

 that portion of the food which enters into the vessels is dis- 

 tributed by them to the various parts of the body, are. questions 

 which will be considered when we come to deal with the generation 

 and nutrition of animals.' 



The constitution of sanguineous animals, so far as the parts as 

 yet mentioned are concerned, and the reasons for such constitution, 

 have now been set forth. In natural sequence we should next 

 go on to the organs of generation, as yet undescribed, on which 

 depend the distinctions of male and female. But, inasmuch as 

 678 a. 



