14 CONSTKUCTION OF THE ABDOMEN. 



The general figure of this cavity partakes of the figure of 

 the lower part of the trunk of the body ; with these exceptions 

 that the diaphragm makes it arched or vaulted above, that the 

 spine and psoae muscles, &c., are rather prominent on the pos- 

 terior surface, and that the lower part corresponds with the 

 costae of the ossa ilia and with the pelvis. 



To acquire a precise idea of this cavity, it is necessary first 

 to study the bones concerned in its structure in their natural 

 situation in the skeleton ; and then the muscles, which form so 

 large a part of it. 



The arrangement of the tendons of some of these muscles, 

 with a view to complete the cavity, is particularly interesting ; 

 as that of the external oblique where it forms the crural arch.* 

 The ligaments of the pelvis and the levatores ani muscles, as 

 they also contribute to the formation of the cavity, and have 

 an influence upon its figure, should likewise be attended to. 



In the walls of the cavity, thus constructed, there are many 

 foramina, by which the viscera and other contained parts com- 

 municate externally ; but few of them pass directly into the 

 cavity ; for, like the thorax, there are no vacuities in it, exterior 

 to the contained organs. 



Three of these foramina are in the diaphragm. One for the 

 transmission of the aorta, another for the vena cava, and a 

 third for the oesophagus. Below, there is an aperture at each of 

 the crural arches, for the transmission of the great femoral 

 vessels ; in each of the ligamentous membranes which closes 

 the foramen thyroideum, for the obturator vessels and nerve ; 

 and at the sacro-sciatic notches, for nerves and blood-vessels. 



There are also two apertures at the bottom of the pelvis, for 

 the orifice of the rectum and of the urethra. In the tendons of 

 the external oblique muscles are two orifices, covered by the 

 integuments, for the spermatic cords ; and, in the foetal state, 

 one for the umbilical cord. 



The apertures in the tendons, and under their edges, for the 



* See the account of this tendon, vol. i. in the description of the " Obliquus 

 Descendens Externus." 



