THE 



CYCLOPEDIA 



OF 



ANATOMY AND PHYSIOLOGY. 



ABDOMEN, (in anatomy,) with which the 

 terms venter and alvus are sometimes used 

 synonymously. Gr. yaarr?^. Germ, bunch, un- 

 terleib, kinterleib. Ital. venire, panda, ubdo- 

 mine : the French anatomists use the word 

 abdomen as we do, and also the term venire as 

 we do belly ; also bas-ventre. It is so called, 

 " quod abdi et tegi soleat, aut quod alimenta 

 in eo abdantur, aut intestina ibi sint abdita."* 



The term denotes a particular region and 

 cavity in a large proportion of the animal series, 

 being found in most of the classes from Mam- 

 malia down to Articulata. It is impossible to 

 give such a definition of this region as will 

 apply to all ; it appears, however, to have one 

 property sufficiently general, viz. that it con- 

 tains in all these classes more or less of the 

 digestive organs. Thus, to ascend from the 

 Articulata : 



It is in the class Insecta of the Articulata that 

 we find the most defined region bearing this 

 name. This region is the most posterior of the 

 three portions into which the body of an insect 

 is divided, and is composed of a series of seg- 

 ments which unite to form a cavity enclosing 

 the viscera subservient to nutrition, respiration, 

 and reproduction ; it does not contain any of the 

 organs concerned in locomotion. It is com- 

 posed of a series of simple hoops, united to 

 each other by a ligamentous connexion, which 

 allows the abdomen to be flexible or otherwise, 

 according to the closeness of the union.f The 

 abdomen is united by its anterior extremity to 



* Facciolati, in verb. 



t See a very good engraving from Carus, of the 

 segments of an insect, in Roget's Bridgewater Trea- 

 tise, vol. i. p. 321. 



VOL. I. 



the thorax. (See INSECTA.) In the Arachnida 

 there is also a similar division of the body, to 

 which the name of abdomen has been applied, 

 united in front with the cephalo-thorax, and 

 separated from it by a deep groove, which 

 leaves only a slender pedicle between them ; 

 like that of the Insecta it contains the principal 

 viscera. (See ARACHNIDA.) 



In all the divisions of the Vertebrata there is 

 an abdomen. In fishes the abdomen is situated 

 towards the posterior extremity of the body, 

 and, is separated from the heart in front by a 

 strong membrane analogous to the diaphragm ; 

 it contains the digestive and generative organs. 

 In reptiles the abdomen is that region which 

 lies immediately anterior to the anus; in many 

 classes it is not separated from the cavity con- 

 taining the lungs, so that the lungs, heart, 

 organs of digestion and generation are all con- 

 tained in one great cavity ; in the crocodile, 

 however, a layer of muscular fibres, having the 

 appearance of a diaphragm, covers the perito- 

 neum, where it is connected with the liver, so that 

 the lungs do not project into the abdomen. In 

 birds, the abdomen extends from the posterior 

 extremity of the sternum to the anus ; it is, as 

 in fishes, separated from the thorax by a mem- 

 brane which, though not muscular, is analogous 

 to the diaphragm, but is perforated so as to 

 allow the air to pass into the abdominal cells. 

 In Mammalia, the abdomen is placed between 

 the pelvis and thorax, with the former of which 

 it is continuous ; but it is separated from the 

 latter by the diaphragm ; its principal contents 

 consist of the digestive organs, and its size 

 varies in reference to their respective degrees of 

 development. 



