178 MALL. [Vol. V. 



S-shaped loop of intestine is cut across three times, and the lesser 

 peritoneal cavity with its communication is shown throughout 

 its whole extent. Within the foramen of Winslow, or rather the 

 communication of the lesser with the greater peritoneal cavities, 

 lies a triangular lobe of the liver, the lobus Spigelii. It arises 

 from the right lobe of the liver, and is surrounded with a space, 

 as shown in Fig. 10. In many respects, the liver of this stage 

 represents the condition found in the adult domestic fowl. 



The omentum from now on rapidly grows, covering all the 

 intestines, but not adhering to the colon, as is the case in man. 

 For the later development I refer the reader to the excellent 

 papers of Muller and of Tolclt. 



In the lower vertebrates the alimentary canal is attached dor- 

 sally by quite a simple mesentery. The same is the case in the 

 embryos of all vertebrates. From this simple, straight mesen- 

 tery, by means of shifting, the later compartments of the ccelom 

 are formed. In the lizard the mesentery is quite simple, 1 and 

 lately Ravn has shown us that on either side of the stomach 

 there is a sack which communicates with the peritoneal cavity, 

 the blind end extending as far forward as the heart. 2 On the 

 right side the opening of the sac is related to the surrounding 

 viscera, as is the foramen of Winslow in birds and mammals. 

 The development of these sacs is not known, but from sec- 

 tions of embryos given by Orr a marked gastric diverticulum 

 is shown. 3 In some specimens of adult turtles which I have 

 examined there is a peritoneal cavity at the lesser curvature of 

 the stomach, which does not communicate with the greater 

 peritoneal cavity. This cavity holds the position of the lesser 

 cavity, and no doubt will prove to be such. Fishes and am- 

 phibia probably have no such cavity. 



From these observations it is seen that the lesser peritoneal 

 cavity is present in reptiles, birds, and mammals. In certain 

 groups of reptiles two diverticula are formed, extending from 

 the pleuro-peritoneal cavity, on either side of the stomach, to 

 the heart. The right is larger than the left, and communicates 

 with the ccelom around the vessels passing to the liver. This 



1 Pittard, Todd's Cyclopadia of Anatomy, Vol. III. 



2 Ravn, His u. Braune's ArcJiiv, 1889. 



3 Orr, Journal of Morphology, Vol. I, PI. XIV, Fig 37, c, PC. 



