MOUTH 



157 



septum seem to persist for a short time, and separate the 'pocket of Rathke, which is 

 of course ectodermic in origin, from an entodermic pouch called SeesseVs pocket, 

 developed from the blind anterior end of the fore-gut. 1 



FIG. 198. FRONTAL VIEW OF THE UPPER 

 PART OF A HUMAN EMBRYO OF ABOUT 

 FIFTEEN DAYS, RECONSTRUCTED 



FROM SERIAL SECTIONS. (His.) *-j'. 



The pericardium is opened to show 

 the heart ; between this and the fore- 

 brain is seen the primitive buccal cavity. 



FIG. 200. FLOOR OF THE PHARYNX OF AN 

 EMBRYO ABOUT FIFTEEN DAYS OLD, AS 



SEEN FROM WITHIN. (His.) 5 y ) . 



The first or mandibular pair of arches join in 

 the middle line ; the second arches are separated 

 by a rounded prominence (tuberculum impar). 

 Behind (below) this is the forked prominence 

 (furcula) bounding a median groove which will 

 become the laryngeal orifice. In the sections 

 of each of the first two arches the included 

 artery is seen. The Roman numerals are 

 opposite the corresponding arches. 



FIG. 199. SKETCH OF A LONGITUDINAL SEC- 

 TION THROUGH THE ALIMENTARY CANAL 

 OF A HUMAN EMBRYO, SOON AFTER THE 

 DISAPPEARANCE OF THE PRIMITIVE 

 VELUM. (His.) * T >. 



The alimentary canal is shaded through- 

 out, uk, section of mandibular arch; 

 BT, hypophysis, behind it the remains of 

 the pharyngeal septum ; Lg, commencing 

 lung, the future orifice of the larynx being 

 opposite K ; Mg, stomach ; 6, liver; Nb, yolk- 

 stalk ; W, Wolffian duct ; _B, blind portion of 

 hind-gut ; all, allantois. 



The remains of this septum have been termed the primitive velum, but the septum has nothing 

 whatever to do with the formation of the permanent velum palati, or with the isthmus of the 

 fauces. The plane of the septum forms in fact an angle with the plane -of the future isthmus 



1 Zimmermann (Archiv. f. mikr. Anat. liii.) has described in a human embryo of four weeks two 

 small vesicles in this region which he regarded as derivations of the pocket of Seessel, and as possible 

 representatives of the preoral gut (v. Kupfferj of lower forms. See also Nusbaum, Anat. Anzeiger, xii. 

 and Bonnet, Anat. Hefte, xvi. 



