156 MR. W. K. PARKER ON THE OSTEOLOGY 



how closely every part corresponds essentially with the like part in the skull of the 

 Common Hen, whilst yet there is much greater delicacy of structure. The occipital 

 plane lies nearly at a right angle with the basi- cranial axis, as in the typical bird : 

 indeed this valuable character is caricatured in the abnormally thick skull of Tetrao 

 urogallus ; in that bird an acute angle is formed between the occiput and skull-base, as 

 in the Pehcan. The Cock of the Woods also differs from its congeners, the smaller 

 " Tetraonince," in having a more ornithically typical vomer and stronger legs. Leaving 

 out this giant of the Grouse-tribe, the rest are very uniform in their structure. The 

 occipital condyle, as in the types, has the form of a deeply dimpled human chin, and is 

 broadest from side to side. Both the occipital and basi-temporal regions are very 

 broad, as in the type, so in the subtype ; and this arises from the most unusual size of 

 the basi-temporal bones below, and of the two superoccipitals above. The only birds 

 approaching the "GaUinse" in the expanse of the skull-base are the "Anatinae;" the birds 

 that rival them in the size of the upper occipital region are the " Struthionidse." The 

 lateral occipitals combine with the basi-temporals to form, in the " Tetraoninse," a very 

 fine, large tympanic bulla, from which, as in the type, the os quadratum is altogether 

 excluded. This total exclusion of the " os quadratum," or developed " incus," arises 

 from the collapse, as it were, of the two incudal crura into one, as in Reptiles, and 

 that one having the relations of the anterior crus, which articulates primarily with the 

 prootic by a small facet, and secondarily with the squamosal by a large reniform condyle. 

 The typical and subtypical Galiinae are peculiar among birds in possessing this most 

 important feature. The orbital process of the " os quadratum " is longer and more 

 delicate in the Grouse than in the Fowl : this process, so well developed in birds, is 

 almost entirely peculiar to them, although a rudiment exists in the larger Ophidians ; 

 nothing of the sort exists on the human " incus ;" and below birds the " os quadratum " 

 ceases to have distinct crura. The tympanic ring is not unfrequently strengthened by 

 distinct bony points, as may be seen in Tetrao urogallus. In some typical forms the 

 external meatus is supported behind by some bony matter ; in Pavo cristatus there is a 

 goodly-sized ossicle in this region. Like the basi-temporal, the "posterior pterygoid 

 processes " of the basi-sphenoid are enormously developed in the Galiinae ; more so, 

 however, in the subtype than in the type. 



The " anterior pterygoid processes " of the basi-sphenoid are in both groups, as in 

 Crax, Talegalla, and the " Anatinae," low and very long, and, as in them, articulate 

 with a corresponding facet on the anterior third of the pterygoid. The basi-sphenoidal 

 " rostrum" is always moderate, much shorter than in the " Struthionidae." In both 

 Fowls and Grouse, as in the Ostrich-tribe, the membranous space between the eyes is 

 small, and becomes filled up with periosteal layers of bone. In both type and sub- 

 type the whole of the facial axis in front of the ethmoid continues unossified ; and in 

 the typical species the alae of the ethmoid and the antorbital plates continue soft 

 throughout life : thus the whole of the nasal labyrinth is lost by prolonged maceration. 



