1901.] NATURAL SCIENCES OF PHILADELPHIA. 255 



be readily understood by referring to the description of tlie car- 

 tilage as given in stage XIII. It suffices to mention that the 

 section passes back of the point where the quadrate curves back- 

 ward on itself, so that the dorsal is the j^roximal, the ventral the 

 distal portion of the cartilage. The distal portion bears the man- 

 dible. Underlying the proximal portion is the Eustachian tube 

 {Eu.), here shown in three detached segments. Other sections, 

 however, show these segments continuous, so that the tube is now 

 complete. jMoreover, the proximal innermost segment is continu- 

 ous with the pharynx and in reality represents a diverticulum 

 (cUv.) from the latter. In the other specimen that I have of this 

 stage this portion is continuous with the pharynx, but its distal 

 extremity ends blindly without forming a connection with the 

 Eustachian tube. In the toad of stage XIII this diverticulum of 

 the pharynx was also present, and connecting it with the widely 

 separated tubal Anlage was a dense strand of connective tissue 

 cells, whose long diameters were extended in a direction coinciding 

 with a line drawn between the separated parts. By means of this 

 diverticulum the tympano-Eustachian tube is now united to the 

 pharynx. The tube presents throughout an irregular lumen, bounded 

 by a well-defined columnar epithelium. That portion of the tube 

 which is most externally situated is the posterior pari; of the 

 tympanic cavity {Tym.). Attached to the dorsal wall of the 

 latter is the columella auris (C/. ). The ramus hyomandibularis 

 of the facial nerve is not shown in this section, since, owing to 

 the posterior flexure of the quadrate and the separation of the 

 hyoid from the latter, the nerve now lies entirely posterior to the 

 tube. 



SUMIMAPvY. 



The results recorded in the preceding pages may be briefly sum- 

 marized as follows : 



1. The tympano-Eustachian passage is in the main derived from 

 the dorsalmost portion of the hyomaudibular fold (cleft). 



2. In the earliest stages described, the hyomaudibular fold is 

 present as a solid, plate-like fold extending outward and forward 

 beneath the eye region and terminating laterally in a free edge 

 situated a short distance below the ectoderm. Its attachment to 

 the ectoderm is lost at about this stajre. 



