435 



find Dear the spot, where in R. esculenta Maueer figures the 

 epithelial knot in question, the attachment of gill filaments to the 

 wall of the branchial chamber, but never any epithelial thickening. 

 The pseudothyroid has a certain fixed relation to adjacent structures, 

 such as blood vessels, nerves and muscles. In consequence the place 

 where it is to develope can be determined early in the metamorphosis. 

 The changes in the branchial apparatus involved in the metamorphosis, 

 although far reaching, are not so great as to prevent the detection 

 of the first anläge of the structure in question. The pseudothyroid 

 is situated between and about the junctions of the Vena mandi- 

 bularis interna and the V. pharyngea with the V. jugular is 

 externa. It receives its blood supply from the ramus musculo- 

 glandularis of the Arteria carotis externa, and venous 

 blood passes from it by several small branches into the Vv. pha- 

 ryngea and j u g u 1 a r i s externa. It is situated anterior to the 

 two "Epithelkörperchen" , although the latter bodies are closely 

 approximated to it in the adult condition. Its relation in all its 

 stages of development to the hypoglossal nerve, to the external 

 jugular vein and external carotid artery, and to the sternohyoid and 

 basihyo-branchial muscles, is such that the supposition that it origi- 

 nated at the close of the larval period from the epitheHum of the 



S" Si, sa, •» « e.-<s 



Fig. 1. Cross-section through the head of a young frog (ß. fusca) of 17 mm 

 length ; parts dorsal to pharynx omitted, a acromion ; ce A. carotis externa ; cp Corpus 

 propericardiale ; cr M. coracoradialis ; dm M. depressor mandibuli ; ds M. deltoideus, 

 portio scapularis; ec epicoi'acoid cartilage; epa anterior "Epithelkörper"; /ig M. hyo- 

 glossus; hy. N. hypoglossus; gl N. glossopharyngeus ; Je V. jugularis externa; m 

 mouth cavity; mk Meckel's cartilage; om M. omohyoideus; pc procoracoid cartilage; 

 ph V. pharyngea; pq quadrate cartilage; prpl j^rocessus postlatcralis of the hyoid 

 cai'tilage ; pHh processus thyreoideus of the hyoid cartilage ; ps pseudothyroid body ; 

 rps recessus lymphaticus pseudothyi-eoideus ; S2)a sinus parahyoideus ; sst sinus sternalis ; 

 ssthy spatium sternohyoideum ; sthy ^I. steruohyoideus ; sthyd M, stemohyoideus, portio 

 dorsalis ; t thymus gland ; th thyroid gland. 



28* 



