No. i.] THE LESSER PERITONEAL CAVITY. 171 



Spigelii now projects markedly into the oral portion of the 

 diverticulum. The portion on the dorsal side of the gizzard has 

 increased with the growth of this organ, and also extends mark- 

 edly into the omentum which partly overhangs the intestine. 

 The whole diverticulum measures, from lung to intestine, three 

 millimetres ; and the gizzard is one millimetre in diameter. The 

 omental cavity is nearly a millimetre wide, and about one-half 

 a millimetre long. It is shown as a distinct cavity, the dorso- 

 ventricular diameter being nearly half a millimetre. 



My material does not suffice to follow the fate of the embryonic 

 omentum. A chick of ten days shows, however, that it is in no 

 way related to the formation of the air sacs. At this stage three 

 large air sacs project from the bronchial tubules into the abdom- 

 inal cavity, representing the number present in the adult. 



The domestic fowl contains three peritoneal cavities, com- 

 pletely separated from one another, and from one of them the 

 lesser cavity arises. The communication is by means of a 

 foramen of Winslow. After the anterior abdominal walls are 

 removed, two ventral cavities are exposed, separated from each 

 other by a vertical longitudinal septum. Into each of the cavities 

 hangs a lobe of the liver, while into the left the ventral surface 

 of the gizzard projects. On the dorsal side of the liver there 

 are, on each side, three air sacs, — an anterior, a middle, and a 

 posterior. The middle is the smallest, and the posterior the 

 largest, and extends throughout the posterior portion of the 

 abdominal cavity. Each sac communicates by means of a 

 special opening directly with the lungs. By allowing the sacs 

 to collapse, we find that a very distinct membrane extends back- 

 ward from the gizzard, and cuts off the portion of the abdominal 

 cavity containing the intestines. This is the "pseudo-epiploon" 

 described by Weldon, 1 and followed more extensively by Bed- 

 dard. 2 A similar membrane is present in crocodiles. In all 

 respects, this membrane is situated in the same position as the 

 epiploon in mammals, with the difference that it is adherent to 

 the abdominal walls along its free border. On the dorsal side 

 of the gizzard the air sacs fill all the space, thus closing off the 

 communication between the cavity in which the intestines lie 

 and the ventral cavities. 



1 Proceedings of the Zoological Society, 1SS3. 



2 Ibid., 1885. 



