ABDOMEN. 



ABDOMINALES. 



and these insects, it may be observed, are also a favourite food of 

 the bear. 



ABDOMEN, the BMy, from atido, to hide, because it conceals or 

 hides its contents. The last syllable is only a termination. The 

 Lower BMy, Imus Venter, Alvus, Gaiter, &c. &c., are synonymous. 



The human body is divided by anatomists into three portions the 

 head, the trunk, and the extremities. The head and trunk enclose 

 cavities which contain the organs or the instruments by which the 

 most important functions of the living body are performed. The trunk 

 forms two cavities, the superior of which is termed the Thorax or 

 Chest, and the lower constitutes the Abdomen. 



In the artificial skeleton nothing is shown, because nothing remains 

 except the mere framework of the body, or the bones ; but in the 

 natural state, when the soft parts remain as well as the bones, there 

 is a complete partition between the cavity of the chest and that of the 

 abdomen (Jig. I., 1, 2). This partition is effected by means of an organ 

 which is termed the Diaphragm (Jig. I., 1, 2), a name derived from a 

 Greek word signifying to divide. The diaphragm is composed partly 

 of membrane, but chiefly of muscle (Fig. II.) It is placed transversely 

 across the trunk at about its 

 middle portion, dividing it 

 into two pretty nearly equal 

 halves (Fig. I.) But the dia- 

 phragm is a moveable body ; 

 it is, in fact, one of the main 

 organs of respiration : its chief 

 function consists in alternately 

 increasing and diminishing the 

 capacity of the thorax and 

 abdomen, for the purpose of 

 respiration. But since the very 

 partition which separates these 

 two cavities from each other is 

 perpetually changing its rela- 

 tive position nowencroaching 

 upon the one, and now upon 2 

 the other it is obvious that 

 their natural capacity must be 

 constantly varying. 



The cavity of the abdomen 

 is bounded above by the 

 diaphragm (Fig. I., 1, 2), below 

 by the bones of the Pelvis or 

 basin (Fig. I., 3, 3), which 

 may be considered as belonging 

 to the bones of the lower ex- 

 i leg, before and at the 

 sides by the abdominal muscles, 

 behind partly by the muscles 

 of the loins, and partly by the 

 bone of the spine. TMopJM 

 is composed of a number of 

 separate bones, each of which is termed a Vertebra. The vertebra; are 

 firmly united together, and by their union form what is commonly 

 called the back -bone, termed by anatomists the Spinal Column, or the 

 Vertebral Column. 



The cavity of the abdomen is lined thi-oiighout by a thin, but dense, 

 firm, and strong membrane, termed the Peritoneum, from a Greek 

 word signifying to extend around. 



We have thus spoken of the abdomen as a cavity, but without 

 explanation this mode of expression may occasion misconception. 

 During the state of life there is 

 co cavity. The abdomen is always 

 nompletelyfcill. It hits been stated 

 that the diaphragm alternately 

 enlarges and diminishes the space 

 proper to the abdomen ; but the 

 abdominal and lumbar muscles, 

 which form so large a part of the 

 boundaries of the abdomen in 

 front, at the sides and behind, in 

 like manner, alternately contract 

 and relax. The consequence is, 

 that a firm and uniform pressure 

 is at all times maintained upon 

 the whole contents of the abdo- 

 men, so that there is always the 

 most exact adaptation of the con- 

 taining to the contained parts, Flo . n.Diaphragm, removed from its 

 and of the viscera one to the natural situation between the Chest 

 other, not the slightest space or and Abdomen, 

 cavity ever intervening, either 



between the walls of the abdomen and its viscera, or between one 



viscus and another. By the cavity of the abdomen, therefore, is not 



t what the expression might at first view seem to denote, namely, 



a void or empty space ; but the term is merely employed to mark 



th extent of the boundary within which the abdominal viscera are 



<ed. 



Fio. I. 



The abdomen, for practical purposes, is artificially mapped out into 

 the following regions. 



Two imaginary lines are drawn across the abdomen, one of which 

 is supposed to extend from about the seventh rib on one side to the 

 same point on the opposite side (Fig. III., 1, 1). The second line is 

 supposed to extend from the fore part of the large bone of the pelvis 

 to the same projecting point on the other side (2, 2). These lines mark 

 out three large and distinct spaces (3, 4, 5). The space above the 

 upper line is termed the Epigastric Region (3). The space below the 

 lower line is termed the Hypogastric Region (5). The space included 

 between the two lines is termed the Umbilical Region (4). 



Two lines are next supposed to extend vertically, one on each side, 

 from between the seventh rib to the prominence formed by the large 

 bone of the pelvis (Fig. III., 6, 6). By these vertical lines the three first 

 regions are still further 

 subdivided in the follow- 

 ing manner : The right 

 and left parts of the 

 Epigastric Region form 

 two distinct regions (7,7) ; 

 these are termed the right 

 and left Hypochondriac 

 Regions (7, 7) ; while the 

 central part retains the 

 name of the Epigastric 

 Region (3). In like man- 

 ner the right and left 

 parts of the Umbilical 

 Region form two distinct 

 regions (8, 8), which are 

 termed the Lumbar Re- 

 gions (8, 8), while the 

 central part retains the 

 name of the Umbilical 

 Region (4). Moreover, 

 the right and left parts of 

 the Hypogastric Region 

 are at the same time each 

 divided into two, which 

 are termed the Iliac Re- 

 gions (9, 9), while the 

 central part is termed the 

 Region of the Pubis (5). 



The term Abdomen, 

 as applied by entomolo- 

 gists to Insects, has a 

 somewhat different signification from the same term when applied 

 to other animals, being used for the whole portion of the body 

 of an insect behind the corselet (thorax), and including the back as 

 well as the belly. It consists, in most cases, of a number of rings 

 without any jointed members for locomotion, and uniformly encloses 

 a portion of the intestines, though sometimes but a veiy small one. 

 These rings, or very short hollow cylinders, are severally united with 

 each other by a joint, by a membrane, or sometimes by an intimate 

 junction, the exact line of which is not very apparent. The rings in 

 some cases, as in the grub of the chameleon-fly, slide into one another 

 like the tubes of an opera-glass. Each ring is technically termed a 

 segment (seg'ment um), virtually composed of two principal pieces, which, 

 when distinct, are termed arches ; the upper the arch of the back, the 

 under the arch of the belly. In some cases these two portions are not 

 distinct, but, when they are so, the two borders usually come into 

 contact. When they do not, but remain free, one usually, more or 

 less overlaps the other, as in bees. In caterpillars, grubs, and wingless 

 insects, such as the flea, where the joining of the corselet with the 

 abdomen is not apparent, the abdomen may always be known by the 

 legs never being jointed with it ; and in caterpillars it usually consists 

 of all the body behind the six fore legs, which are always on the 

 corselet. 



ABDOMINALES, in Zoology, the name of a group of fishes, to which 

 different naturalists have attached a more or less extensive signification, 



FIB III. 



Salmon, given as a specimen of the family of Abdominalcs. 



The 



according to the particular principles of their several systems. Tl 

 classification of fishes given by Linnaeus is founded upon the presen- 

 and position of the ventral fins (those of the belly) in relation to the 



