14 



PEOr. D ARCy W. THOMPSON ON THE 



[Jan. 1 



<5 



the antero-posterior groove that constitutes the unusually simple 

 glenoid cavity of the mandible. In front of this lower articular 

 margin of the quadrate is a small but distinct rounded head or 

 condyle for the pterygoid. An anterior process, small, short, and 

 sharply pointed, runs forwards, at an obtuse angle to the shaft of 

 the bone. The shaft has two heads, the external or squamosal one 

 being large, the inner or prootic one much smaller and separated 

 from the outer by a very shallow groove : a pneumatic foramen 

 enters the shaft on its inner side, below the prootic capitulum. A 

 cup for the quadrato-jugal articulation is directed outwards and 

 forwards, and stands elevated on a tubercular mass of bone, whose 

 posterior surface forms a conspicuous ridge ; on the sloping ridge 

 below the cup is a small accessory articular surface, which plays 

 against the edge of the mandible (c/. Mivart, pp. 374, 391), and 

 whose comparative anatomy is more fully discussed below. "We shall 

 find that the quadrate is markedly different from this in Stringops; 

 and that in the other genei'a considerable but less important differ- 

 ences exist in the greater or less separation of the two capitula, 

 the size of the anterior process, the distinctness of the pterygoid 

 condyle, and the conformation of the parts adjacent to the quadrato- 

 jugal cup. 



Family Jsestokid.i:. 



In all the characters with which this paper is mainly concerned 

 the skull of Nestor (figs. 3, 6) is extremely interesting. 



The orbit is incomplete. The postfrontal process is rudimen- 

 tary ; the prefrontal process is long, evenly curved, and reaches 

 nearly to the squamosal. The squamosal region is entirely dif- 

 ferent to that of any other Parrot. The squamosal or zygomatic 



Nestor notahUis. 

 pj., postfrontal process ; sq^., squamoBal. 



process, instead of being slender and free on its lower or posterior 

 margin, is continuous with a flattened buttress of bone which 

 connects it with the main body of the squamosal, and which descends 



