1901.] NATURAL SCIENCES OF PHILADELPHIA. 253 



nectiou ^vitll the pharyngeal wall, Jjut immediately internal to its 

 proximal termination the pharynx sends out a narrow cleft between 

 the hyoid and the base of the auditory capsule. Posteriorly the 

 tube ceases immediately in front of the dense strand connecting 

 the hyoid cornua with the auditory capsule, so that at this stage the 

 tube occupies its definitive position between the quadrate and hyoid 

 cartilages. As a result of the changes that have taken place in 

 the hyoid its nerve, the ramus hyomandibularis, now lies ventral 

 and posterior to the tube — a position which characterizes it in the 

 adult condition. lu the branchial region the entire branchial 

 apparatus, including the " lateral recess" of the pharynx, has be- 

 come largely obliterated. 



Stage XIII. — Young toad, G mm. Metamorphosis complete. 



This period marks the close of the metamorphosis. The infe- 

 rior, articular portion of the quadrate extends more posterior, so 

 that the quadrate on its posterior surface shows a marked con- 

 cavity. The general course of the quadrate is about as follows: 

 Dorsally from its union with the base of the auditory capsule it 

 extends forward and downward for some little distance, it then 

 describes a wide curve downward and backward for the remainder 

 of its length, so that its distal end, bearing the mandibular car- 

 tilage, now comes to lie under or even slightly behind its dorsal, 

 proximal extremity. Tiie hyoid arch is now fused completely with 

 the auditory capsule, the intervening cellular strand having become 

 cartilaginous. 



The annular cartilage is now located posterior to the eye and 

 ventral to the anterior portion of the auditory capsule. It closely 

 underlies the skin and is external to the outer surface of the 

 quadrate. The Eustachian tube itself differs but little from its 

 condition in the preceding stage, except that its lumen, where 

 present, is more distinct and extensive. A short distance above 

 the tube the distal extremity of the columella auris may be observed 

 as a dense cellular mass, which posteriorly grades into true car- 

 tilage. 



Stcuje X/F. — Young toad, about 9 mm (figs. 30, 31). 



In this stage the tympano-Eustachian passage has the same 

 general position and relations that distinguish it in the fully mature 

 animal. Relatively it is not so large as in the latter, nor is its 

 lumen complete throughout, but in all other respects it is essentially 



