13 ABDOMEN. 



thorax, and thus these muscles must be con- ful parts of the mechanism of the abdominal 

 sidered as very important agents in the act of muscles. This is mainly to be attributed to 

 expiration. It must be observed, however, the close connection which subsists between 

 that in order that they may act on the chest these muscles in consequence of the formation 

 with their full force, it is necessary that that of the sheaths of the recti by their aponeuroses, 

 cavity should have been previously in a state and the adhesion of the anterior wall of those 

 of full dilatation, for under such circumstances sheaths to the tendinous intersections of the 

 the fibres of the obliqui and recti are con- recti. When the recti contract, the antero-pos- 

 siderably stretched and their levers elongated.* terior diameter of the abdomen is diminished, 

 It is in the excited states of expiration, cough- and consequently the viscera are pushed to- 

 ing, sneezing, &c., that this action of these wards the sides ; when, on the other hand, the 

 muscles is most obvious. obliqui contract, they diminish the transverse 



But it is in the motions of the trunk that diameter of the abdomen, and push the viscera 

 the abdominal muscles are called most into forward in the middle line. In the one case, 

 play. In all the inflexions of the trunk, whe- then, it will be evident that the obliqui act as 

 ther the body be horizontal or erect, these moderators to the recti, and in the other the 

 muscles are main agents. When the body is resistance of the recti moderates the action of 

 recumbent on a horizontal plane, the recti are obliqui, the former muscles being, as Cru- 

 thrown into action when the individual attempts veilhier remarks, as it were, two active pillars 

 to raise up the thorax, the spine being thereby compressing forcibly the viscera against the an- 

 brought in to the state of flexion. If the thorax be terior surface of the spine. It is probably to 

 fixed, while the body is still supine, the action enable the recti to act more completely as 

 of the recti will draw the pelvis upwards and moderators upon the several segments of the 

 forwards, causing slight flexion of the spine, obliqui that they are intersected by tendinous 

 and slightly approximating the upper margin lines, with which the aponeuroses of those muscles 

 of the pelvis to the lower margin of the thorax, are connected. Another use has been assigned 

 Although the recfi muscles are the principal to these intersections by Berlin, viz., to multi- 

 agents in thus flexing the spine, the obliqui co- ply the points of attachment of the obliqui 

 operate with them very powerfully, and are muscles, and to associate them, in many ac- 

 especially useful in maintaining the due propor- tions, with the recti muscles. This is explained 

 tion between the middle and lateral regions of by a reference to the action of the recti in flex- 

 the abdomen. When the two obliqui of the ing the pelvis : were these muscles uncon- 

 same side act together, the direction of their nected with the obliqui, they would act only 

 force is, as with all oblique muscles whose on the pelvis, into which they are inserted ; but 

 fibres decussate, in the diagonal between their in consequence of the insertion of the internal 

 fibres; and, therefore, when the obliqui of op- oblique into the intersections of the recti, and 

 posite sides act in unison, they very powerfully the attachment of that muscle also to the crista 

 aid the recti in flexion of the spine, approx- ilii, the force of contraction of the recti is com- 

 imating the thorax and pelvis anteriorly. When municated not only to the pubis, but also 

 the obliqui of one side act, they produce a through the fibres of the obliquus internus to 

 lateral inflexion of the trunk to that side, the the rest of the pelvic margin.* 

 middle and opposite region of the abdomen The action of the pyramidales seems to be 

 being in this position rendered prominent by chiefly on the linea alba, which they render 

 the viscera pushed over from the side of the tense ; thus limiting the separation of the recti, 

 contracted muscles. In what have been called and opposing the tendency to visceral protru- 

 the rotatory motions of the trunk, the obliqui sion. Fallopius supposed that they acted on 

 muscles of the same side antagonize each other; the bladder, especially when it was in a dis- 

 thus in that movement by which the anterior tended state ; and Parsons conjectured that 

 surface of the trunk is made to look to the left they might depress the suspensory ligament of 

 side, the obliquus externus of the right side will the bladder (the urachus), and thus facilitate 

 co-operate with the obliquus internus of the the contraction of that organ, 

 left, but the obliquus internus of the right will The other muscles which are from situation 

 antagonize the external muscle of the same abdominal muscles in consequence of their 

 side. " These muscles," (obliqui externi et in- connexion with the posterior wall of the abdo- 

 terni,) says Dr. Barclay, " from occupying men, are chiefly agents in the extension of the 

 the whole of the lateral aspects extending be- vertebral column : in their contracted state, 

 tween the ilia and ribs, and from acting at the however, they form a tense and resisting sur- 

 greatest lateral distance from the centre of face, against which the viscera are compressed 

 motion, must always be muscles principally by the contraction of the anterior muscles, 

 concerned in producing inflexions dextrad and II. Of the Abdominal Cavity. The annexed 

 sinistrad on the lumbar vertebrae, principal di- engraving (fig. 5.) exhibits a view of the abdo- 

 rectors in all the inflexions sternad and dorsad ; minal cavity, the anterior and part of the lateral 

 and, from the assistance which they give to the walls having been cut away and the viscera 

 recti, principal librators also of the trunk, whe- removed. The subject is so bent backwards 

 ther we be sitting, standing, or walking." as to render the bodies of the vertebrae very 



The reciprocal action of the recti and ob- 

 liqui on each other is one of the most beauti- * Berard> loc> cit>> et Bert5n> sur rusage des 



enervations des muscles droits du bas-ventre, in 

 : Barclay on Mascular Motion, p. 522. M(?m. de 1'Acad. des Sciences de Paris. 



