12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



hypophysis is here cut laterad to its median plane, so that its stalk 

 is not shown. The lateral outgrowths from the median body are 

 now more numerous, more than a dozen being cut by the plane of 

 this section. Some of these outgrowths still exhibit a small, circular 

 lumen, while others are solid. The outgrowths lying next to the 

 infundibular wall are crowded very close together, while those nearer 

 the pharynx are separated by considerable connective tissue. 



No sign of the pharyngeal sac is seen in this section. 



Figure 5c is through the median plane of the hypophysis. The 

 hypophysal stalk, h. s., is here cut throughout its entire length ; its 

 connection with the oral epithelium is still evident and complete, but 

 its lumen has entirely disappeared. The stalk, though narrower 

 than in the preceding stage, is more than twice as long, and is 

 slightly bent towards an S shape. A considerable cavity, h., is still 

 seen in the body of the hypophysis, and two of the outgrowths, 0. and 

 0'., are evident. The position of the outgrowth 0". is seen as a small, 

 nearly solid projection close under the wall of the infundibulum. 

 Just to the right and below (as seen in the figure) the outgrowth 0". 

 is seen a larger mass, 0"'., elongated in outline and with a narrow 

 lumen (a small, round hole in this section). Although in close 

 contact with the front wall of the body of the hypophysis, this thick- 

 walled vesicle seems to have no direct connection, at this stage, 

 with the rest of the hypophysis. 



The greatest length of the body of the hypophysis is now about 

 0.75 mm., an increase of 0.25 mm. over the preceding stage. Owing 

 to a failure to record the thickness of the sections of this series the 

 width of the hypophysis could not be determined. 



A well-marked invagination,/'.^., of the pharyngeal wall, a short dis- 

 tance back of the hypophysal stalk, may represent the pharyngeal sac. 



From the floor of the infundibulum, in., a deep, narrow pit, in'., 

 projects down into the body of the hypophysis. The bottom wall of 

 this pit is in close contact with the cells of the hypophysis, perhaps 

 continuous with them, but no opening from infundibulum to hy- 

 pophysis can be made out. 



Figure 6a shows the condition of the hypophysis in an embryo of 

 about 6 cm. length. The stalk, h. s., is very long and still more 

 slender and curved than in the preceding stage ; it connects with the 

 surface at the base of a backwardly projecting fold of skin, the 

 eustachian valve, e.. The stalk not only shows no sign of a lumen, 

 but is actually discontinuous at a point near its middle region. 



The body of the hypophysis is little if any larger than in the 

 preceding stage ; its cavity has almost completely disappeared, being 

 seen only as a narrow slit in one or two regions. 



