100 BULLETIN OF THE ESSEX INSTITUTE. 



The entire absence of a stapes in the history of the 

 chondrocranium is the only noteworthy point of difference 

 between the formation of the ear capsules in Desmogna- 

 thus and in Amblystoma. The trabeculse and quadrates 

 present conditions essentially the same as those of a cor- 

 responding stage in Amblystoma, but owing, in part at 

 least, to the early appearance of the bony skull in Des- 

 mognathus no complex nasal capsule is formed. The 

 simple condition shoAvn in Fig. 14 is the highest state of 

 development reached by the anterior ends of the trabecu- 

 Ise. A small antorbital process develops in the usual place 

 upon the side of the trabecula. No pterygoid process of 

 the quadrate appears in either of the stages modelled. 

 As the older stage presents a state of development ap- 

 proximately equivalent to that found in the fifth stage of 

 Amblystoma the appearance of this process as figured by 

 Wiedersheim ('77) must be a comparatively very late 

 occurrence. 



Plethodon glutinosum (Fig. 15). 



From a specimen of Plethodon glutinosum twenty mm. 

 in length and showing the chondrocranium in an advanced 

 stage of development, I have modelled the nasal capsules. 

 In regard to the rest of the skull mention of a few points 

 will suflice. 



In the main it corresponds closely with the skull of 

 Amblystoma as described in our fifth stage (Figs. 12 and 

 13). This similarity is especially noticeable in the posi- 

 tion of the pterygoid process. There is a stapes, the 

 antero-dorsal point of which, unlike that of Amblystoma, 

 is connected to the quadrate by a very slender stapedial 

 process. The otic and palato-basal processes present the 

 usual conditions. 



Aside from the rod connecting the dorsal and ventral 



