26 GENERAL HISTORY OF BIRDS. 



small bones found in the middle ear; and the circlet of ossifications found 

 in either eye, termed the sclerotal plates. Often there are additional ossifica- 

 tions, as the supraorbital bones in the diurnal raptores; the nuchal style in 

 the cormorants; and not a few others. Frequently too, the lacrymal bones are 

 not united to the skull. 



This is the case of the common fowl wherein we often find the pre- 

 maxillary, the nasals and the vomer independent bones; the latter, when it 

 ossifies, invariably so. The larger and posterior part of the skull fuses into 

 one piece, designated as the cranium, the bones composing it entering into the 

 formation of the brain-case, or brain-casket, it being the osseous box in 

 which the brain is enclosed, and by which it is protected. At the base of the 

 cranium upon either side, there are also found the ear-cavities. Either of 

 these offers a conspicuous entrance below the squamosal bone while in front 

 of the opening we meet with the quadrate ione, a freely articulated segment 

 that stands between the cranium above, and the articular cup intended for its 

 reception at the free posterior extremity of either limb of the lower jaw, or 

 mandible, below. From either quadrate there passes forward a slender 

 bar, — the quadrato-jugal bar — that has a free articulation with the quadrate, but 

 anteriorly is wedged in between the nasal and the premaxillary. It is com- 

 posed of three separate elements, and it bounds the cavity of the orbit beneath. 

 This latter cavity is separated from its fellow of the opposite side, by a bony 

 partition called the interorbital septum, largely composed of the mesethmoid. 

 In many birds the cavity of an orbit and the nasal or rhinal cavity in front of 

 the former, are more or less completely separated by the ethmoidal lateral 

 wings, known as the pars plana on either side, while the turbinal bones of the 

 nasal chamber often ossify to a greater or less extent. They hardly do at all 

 in the fowl where all that part of the skull is very open and exposed in the 

 dried adult preparation, though in other birds, as in the Parrots and Falcons, 

 the very reverse of this state of things obtains. 



In the fowls we note what corresponds in other vertebrates to the external 

 openings of the nostrils — the external narial apertures, — are large and oval in 

 outline, their curves being continued to include the free anterior margins of the 

 nasal bones. When this is the case the bird's skull is said to be "holorhi- 

 nal". In some forms, however, the curve is broken as it comes to the nasal 

 bone, which latter exhibits a clef t or fissure;. — such skulls being termed "schizo ■ 

 rhinal", and birds possessing them, schizorhinous. By some anatomists this 

 character has been used in classification, where in many instances too much 

 significance has been attached to it. The upper bill or beak of a bird, techni- 

 cally termed its superior osseous mandible, is, for its entire anterior portion, 

 formed by the premaxillary bone. This is one of the most interesting ele- 

 ments of the skull, and is a bone that occurs in the skulls of every form 



