STUDIES OP THE MACROCHIEES. 



323 



of the walls of this part of the cranium and how thin they are. 

 Air seems to gain access to the major portion of the skull in both 

 of these specimens, including the quadrates and perhaps the 

 pterygoids. 



I am reminded in my examination of the mandible of Trogon 

 of the form this bone assumes in some of the smaller American 

 Owls, as ^peotyio for example. Its articular ends are rather 

 large, being bluntly pointed behind, and having long, sharp, in- 

 turned mesial tips. 



The borders of the rami are rounded ofl', while their height 

 remains quite uniform for the entire length of the jaw. Upon 

 their outer aspects, for the posterior moiety of each, an excavation 

 occurs, at the middle of which, on either limb, is seen a small 

 ramal vacuity. 



The symphysis is deeper by half again than either ramus, and 

 the superior border above it is sharpened. In general outline the 

 mandible of a Trogon is broadly V-shaped, and this bone is partially 

 pneumatic. 



So far as these two specimens are concerned, I find that T. 

 puella differs from T. mexicanus in its skull in having an entire 

 osseous nasal septum, a rather wider frontal space on the superior 

 aspect of the skull between the orbital margins, the parietal 

 eminences are not so lofty, and a better developed osseous lip 

 protects the entrance to the Eustachian tubes. Their mandibles 

 are essentially similar. 



Of the Hyoid Arches. — As might be expected, these practically 

 present little or no difference in the two species of Trogons 

 before me. The hyoid arches in T. mexicanus are small as com- 

 pared with the size of the skull of the bird, the thyrohyals barely 

 curving up behind at all. The apparatus as a whole reminds me 

 not a little of the hyoid arches in some of the smaller American 

 Owls {Glaucidium). 



The glossohyal is formed entirely of cartilage, while the 

 ceratohyals have ossified. In this adult bird the first and second 

 basibranchials are joined in one piece by anchylosis, the cerato- 

 branchial of the thyrohyals apparently articulating in the lateral 

 sockets at their point of union. 



Cartilaginous tips finish off the hinder ends of the epibranchials, 

 and these elements of the " greater cornua " are nearly straight 

 longitudinally, nor are they notably curved in the direction of 

 the median plane of the body. 



