THE RESPIRATORY APPARATUS 203 



ing from the spine to the pelvis. Anteriorly these sacs adjoin the 

 diaphragm, the testes in the male, and ovary in the female, and to 

 the parietes of the abdomen and those of the pelvis. Below and in 

 front, they rest on a fibrous septum, which in all birds divides the 

 abdominal cavity into two smaller cavities: one anterior, represent- 

 ing the abdomen and containing the liver; the other posterior, 

 representing the pelvis and containing the gizzard and the intestines. 

 The anterior portion overlies the posterior part of the lobes' of the 

 liver, the proventriculus, the spleen, and the gizzard. The kidneys 

 are located above these air-sacs. Dorsal to the sacs is also a part of 

 the intestines and in the female the oviduct. The abdominal air- 

 sacs are attached by a ligament-like structure in their medial, their 

 anterior, and their lateral margin. The posterior, the dorsal, and 

 the ventral margin are free. Mesially this attachment is to the 

 mesentery, connecting the left caecum to the dorsal margin of the 

 gizzard, and also to the mesentery of the proventriculus. The 

 anterior attachment is to the body wall and extends in front of the 

 end of the ovary and the adrenal glands. At the antero-lateral part 

 of the body cavity the attachment extends in a widening band along 

 the lateral side of the ovary and of the oviduct, as far back as the 

 caudal margin of the sac. The lateral attachment is related to 

 the kidney, the dorsal ligament of the oviduct, and the abdominal 

 wall. 



Each of these abdominal sacs has three extensions: one supra- 

 renal and two femoral. 



The suprarenal extension leaves the principal sac at the postero- 

 external part of the kidney, extends upward, and forward, and 

 expands over the surface of the kidney. At the internal border of 

 the kidney, this prolongation extends between the transverse 

 processes of the sacral vertebrae, reaches a height of the first dorsal 

 vertebra, forms a triangular canal located above the sacrum in 

 the sacral channel, and is separated from its fellow by a series of 

 corresponding spinous processes. 



The two femoral extensions, an anterior, small, and a posterior, 

 large, extend from the abdominal air-sac at the cotyloid cavity, leave 

 the pelvis through the bony passage occupied by the crural vessels, 

 extend around the coxo-femoral articulation, and terminate in a 

 blind extremity. In some birds, particularly in birds of prey and 

 ostriches, there are prolongations extending into the femur, entering 

 through a foramen at the anterior part of the great trochanter. 



