OCR Text |
Show 1905.] OSTEOLOGY OF THE EURYL EMTD^E. 33 Passeres. In shape and position, however, this group of foramina more nearly resembles its counterpart in the Bucconidse. These foramina form a sort of cribriform plate guarding the mouth of the recessus tympanicus posterior, which is much reduced. The recessus tympanicus superior is of small size, and opens externally into the tympanic cavity by a small aperture lying between the squamosal and otic heads of the quadrate. The aperture is bounded externally by a short, pointed processus articularis squamosi. The Squavioscd Prominence.-It has already been pointed out (p. 32) that the constriction of the temporal region of the cranium has given the tympanic region a sort of individuality not met with in the skulls of the higher Passeres, but common among the lower types, and among the Ooraciiformes. In the Eurylsemidse the free edge of this prominence projects shelf-like beyond the head of the quadrate. It is continued forwards into a hastate processus zygomaticus squamosi directed downwards and outwards. From the base of the inferior surface of this process projects a short pointed processus articularis squamosi; between these two processes the head of the quadrate is firmly grasped. The temporal fossa} are especially deep in Cory don. As in other genera, they are linguiform in shape and do not extend inwards beyond the outer border of the supraoccipital fossa. The trigeminal foramen pierces the skull-wall at about the level of the otic articular process for the squamosal, but some considerable distance mesiad thereof. The orbito-sphenoid does not ossify. The interorbital septum is largely fenestrated. The interorbital region of the frontals is generally very narrow so that the orbits are only very partially roofed. In front the orbit is bounded by a [--shaped antorbital plate. In Calyptomena the interorbital region is wide. The lachrymal, in Calyptomena (PL II. fig. 2, I.), has the form of a sigmoid rod more or less clubbed at each end. The upper end would perhaps more correctly be described as hammer-shaped, and is completely overshadowed by wide expansions of the frontal. The whole ossicle is embedded in a groove carved out of a very much swollen antorbital plate. The close resemblance between the lachrymal of Calyptomena and that of Chasmorhynchus is most remarkable. Both are embedded in the antorbital plate, and both have the same sigmoid flexure. Only in the larger size of the orbital end can the lachrymal of Chasmorhynchus be distinguished from that of the Eurylsemid Calyptomena. In all the other Eurylsemidse, however, the lachrymal appears to have been lost; further, the antorbital plate has been reduced to a thin |-shaped plate. The Ethmoidal Region.-The mesethmoid is greatly reduced by the fenestration of the interorbital septum. The antorbital plate which bounds the orbit in front is |-shaped and attached to Prog. Z ool. Soc-1905, V ol. II. No. III. 3 |