13S A HUMAN EMBRYO OF TWENTY-FOUR PAIRS OF SOMITES. 



tioii and a figure which he published later (1908). In 1908 he wrongly identified what is 

 actually the lung-bud as the stomach, and 1907 he placed the lung-bud in the region of 

 the diverticulum, which I have identified as a questionable fifth pharyngeal pouch. In 

 fact, the embryo has as yet no indication of the stomach. Moreover, his model was 

 probably made on too small a scale." 



The longitudinal groove which Grosser 15 describes extending from the region 

 of the last pouch down to the lung-bud is not present in my specimen. 



According to Lewis 28 , the Bremer embryo possesses a definite pyriform lung- 

 bud, which is directed ventrally and caudally. The Broman embryo of 4.25 mm., 

 as figured by Grosser 15 , shows a similar lung-bud. 



GASTRIC REGION. 



For the following unpublished statement concerning the gastric region of the 

 Bremer embryo I am indebted to Professor Lewis : 



"In the Bremer embryo a gastric region may be referred to, but it is not marked off 

 in any way from the esophagus or duodenum. It may be located only by its relation to 

 the liver and body cavities. It is a flattened or laterally compressed tube, having a cleft- 

 like lumen." 



From the condition found in the Bremer embryo, which is undoubtedly older 

 than mine (having limb-buds), it would seem that the presence of a stomach in 

 my specimen is improbable. A pulmonary diverticulum is to be expected. It 

 seems to me, therefore, more reasonable to interpret the lower swelling, from its 

 relation to the hepatic diverticulum, lying above the transverse septum and 

 consequently in the pleuro-pericardial portion of the ccelom, as the lung-bud. 

 The divided swelling situated above the pulmonary diverticulum probably cor- 

 responds to Grosser's doubtfully identified fifth pouches, but I am unable, from 

 my specimen, to confirm Grosser's interpretation of its significance. That portion 

 of the foregut between the lung-bud and hepatic diverticulum presumably cor- 

 responds to what Lewis 28 has designated the gastric region. A cross-section of 

 this region is shown in text-figure 4. 



HEPATIC DIVERTICULUM. 



A short distance below the gastric region the gut widens out considerably, 

 forming a third diverticulum, the liver (text-fig. 5, and plate 3, figs. 3 and 4). 

 It is directed ventrally and orally. It presents at about the junction of its lower 

 and middle thirds a broad, shallow, transverse groove which divides the diver- 

 ticulum into two portions, both entirely embedded in the septum transversum. 

 Extending ventrally and laterally from the upper portion are a number of buds, 

 the beginnings of hepatic trabeculse; no such buds are found in connection with 

 the lower part. The buds are composed of proliferating epithelial cells which, as 

 indefinite cords, have invaded the mesenchyma of the septum transversum. Most 

 of them are indistinct and their extent is doubtful, for their cells closely resemble 

 those of the mesenchyma and there is no definite line of separation between the 

 two, such as a basement membrane. They are readily overlooked, and it is only 

 with an oil-immersion lens that they are made out with any degree of certainty. 



