OSTEOLOGY OF BIRDS 



347 



this cuckoo ever possesses these delicate elements they must be very 

 small, as there is scant space for them where they ought to occur. 

 I find them pretty well developed in Cuculus c a n o r us , how- 

 ever, and long ago Forbes found them in other cuckoos. 1 



An orbit is not only capacious in the matter of size, as in the 

 trogons and goatsuckers, but its osseous walls are unusually com- 

 plete, a fact due to the presence of the large, quadrate pars plana in 

 front and the diminutive foramina for the exit of nerves from the 

 brain cavity, posteriorly. The floor of this orbit, however, is quite 

 incomplete, as both a pterygoid and a palatine are very narrow and 

 slender bones, and thus contribute but very little osseous surface. 

 All of this holds true for Cuculus in which genus the pars plana is 

 markedly perfect. This osseous insufficiency of the floor of the orbit 

 constitutes one of the striking differences between the skull of a 

 typical cuckoo and a typical goatsucker (Caprimulgus) , as in the 

 latter group the palatines and other bones in that region are un- 

 usually broad, a fact pointed out both by myself as well as others. 2 



As in Cuculus and Coccyzus the zygoma, or that portion of it 

 which constitutes the infraorbital bar, is slender, being compressed 

 from above downward for its anterior moiety, and from side to side 

 posteriorly. Its distal end or the maxillary is broadly expanded as 

 a horizontal triangular osseous plate, thus forming a large part of 

 the floor to the rhinal chamber. At its proximal extremity, the facet 

 for the quadrate is very weak and diminutive, while between it and 

 the articular end of the mandible on its outer side is wedged in a 

 free, subelliptical mandibular sesamoid, of some size. This is also 

 present in Cuculus, and probably in the American genus Coccyzus, 

 although I do not seem to have described it in my paper giving 

 the osteology of those birds. The large, subcirc.ular auricular aper- 

 ture, is much exposed in the dried skull, being only to a slight extent 

 overshadowed by the outstanding squamosal process and exoccipital, 

 posteriorly, and the quadrate in front. A wide crotaphyte valley 

 stands between the two lateral processes in this region of the 

 cranium, which is well marked, being extended posteriorly as the 

 broad crotaphyte fossa, which in the supraoccipital region is sep- 

 arated from the fossa of the opposite side by about a centimeter's 

 interval. Comparatively, this interval is much greater in Cuculus, 



1 Forbes, William Alexander. Collected Scientific Papers. Lond. 1885. p. 415. It 

 is not stated here in which cuckoos the ossicle was found, and in any event it ap- 

 pears to be quite inconstant. 



2 Owen, Sir Richard. Comparative Anatomy and Physiology of Vertebrates. Lond. 

 1866. 2: 52. 



