BY W. J. McKAY. 907 



The bone articulates with the parietal, quadrate, prootic, epiotic, 

 and supraoccipital. 



Os QUADRATUM. 



Quadrathein, D'Alton ; Qimdratum^ Gegenbaur, Hallmann, 

 Huxley, Joh. Miiller, Parker, Hoffmann, Parker and Bettany, 

 Rathke, Wiedersheim ; Quadratum vel Tympanicum, Owen, 

 Stannius, Cuvier. 



The quadrate is a prismatic-shaped bone with two articular 

 extremities. The bone is twisted on its vertical axis from before 

 outwards and backwaras. The external side commences in a fiat 

 oval surface above, and runs downwards and backwards to end 

 below in an external condyle. The posterior temporal muscle 

 arises from the upper three-fourths of the surface. The posterior 

 side commences as a slightly concave surface above, and runs 

 downwards and backwards, and ends below in a flattened surface. 

 The digastric muscle arises from this surface. The internal side 

 begins above as a broad concave surface ; it runs downwards and 

 outwards, and inferiorly coming to lie anteriorly, owing to the 

 twisting of the bone. The external pterygoid muscle arises from 

 this surface. There are three edges to the bone. The posterior is 

 the only one that calls for notice. It projects forwards, and 

 curling round forms a concave surface, to the middle of which 

 the columella and the stylohyal are united, and it also serves to 

 give origin to the external pterygoid muscle and the suboccipital 

 articular muscle. 



The superior extremity is prismatic in outline. The external 

 and anterior faces are the continuations upwards of the exterior 

 and anterior faces of the shaft of the bone. The internal face is 

 oval, concave from before back, broader anteriorly than poster- 

 iorly. It articulates with the facet on the external surface of 

 the squamosal, a small synovial membrane being present. The 

 lower surface is flattened from before backwards, and presents a 

 striking similarity to the inferior extremity of the humerus of the 

 human body. There is a small external and internal condyle, and 

 a trochlear surface. The external condyle is sub-cutaneous. To 



