592 B. F. Kingsbuiy and H. D. Keed. 



Figs. 54-55; PL VIII, Fig. 56) which was at our disposal. The 

 squamosum, furthermore, is the only skeletal element to which the 

 columella is attached, save the os pterygoideum which works its way 

 well up on the inner surface (PI. VII, Fig. 54) of the palatoquad- 

 rate and whose upper edge is somewhat loosely connected with the 

 end of the stilus columella?. As though determined by the excessive 

 flattening of the head in this form, the mandibular end of the 

 palatoquadrate is well back and lateral, while the cranial attachment 

 by means of the usual three processes is unusually far forward 

 (cephalad). The whole suspensorium is therefore rotated from an 

 '4deal" transverse position, and it would seem as though this dis- 

 placement might well explain in a mechanical way (a) why the 

 stilus columellse joins the under surface of the squamosum instead 

 of its caudal edge as in so many of the forms ; (b) how it is possible 

 for the OS pterygoideum to come into such close relation to the 

 columella; (c) the absence (in the young adult at least) of a con- 

 nection of the stilus with the palatoquadrate or os quadratum.-^*' 



A second interesting feature found in this skull is the presence of 

 what might be interpreted as a Ligamentum hyo-columellare (PI. 

 VII, Fig. 55, L. h. c.) which is essentially a thickening of the 

 fascia covering the inner (under) surface of the M. cephalo-dorso- 

 mandibularis. It extends from the ceratohyal to the outer surface 

 of the stilus, extending with it to its attachment to the squamosum. 

 As this ligamentous thickening of the fascia is relatively more marked 

 in the larva, it will be mentioned again in connection with that 

 stage. 



The columella appears to ossify in the typical way ; at the stage 

 of our specimen it consists of a cartilaginous body (PI. VII, Fig. 

 55 ; PI. VIII, Fig. 56) with an inner and outer plate of perichondral 

 bone, the latter extending out upon the stilus for a distance. The 

 distal portion possesses no bony sheath and it was doubtless this that 

 led Parker to distinguish here two elements, a Stapes (bony and 



'*From this bone as a center the ossification of the quadrate cartilage appar- 

 ently proceeds. Kingsbury referred to it as "bone X," Gaupp has suggested 

 tentatively the homology with the os quadrato-maxillare of Anura. Its final 

 interpretation requires additional comparative investigation. 



