0. C. Marsh — -The Skull and Brain of Claosaurus. 85 



squamosal, but its distinct, rounded head indicates the possi- 

 bility of some motion. On the outer surface in front, it joins 

 by open suture the strong jugal bone, and below this, unites 

 with the small, discoid quadrato-jugal. Its inner margin 

 extends forward into a broad, thin wing for union with the 

 pterygoid. The lower extremity is massive, and moderately 

 expanded transversely for articulation with the lower jaw. 



The jugal is one of the most characteristic parts of the skull, 

 as may be seen from the figures on Plate IV. Its main por- 

 tion is robust, much compressed, and convex externally. On 

 its upper margin, it forms the lower border of the orbit and 

 of the infra-temporal fossa, sending up a strong process between 

 them, which extends inside and in front of the postorbital 

 branch of the postfrontal. In front, it is strongly united to 

 the maxillary, and above joins by suture with the lachrymal. 



T*ne maxillary bone in Claosaurm is of moderate dimen- 

 sions, and seen from the outside is overshadowed by the pre- 

 maxillary and jugal, as shown in Plate IV, figure 1. Its 

 lower dentary border is thickly studded with a regular series of 

 teeth, which slightly overlap those of the lower jaw. From 

 above, only a small portion of the maxillary is visible, as seen 

 in Plate V, figure 5, m. 



The lower jaws are long and massive. The predentary 

 bone is robust, and especially fitted for meeting the strong 

 beak above. The dentary bones are large and powerful, with 

 elevated coronoid processes. The angular and surangular 

 bones are, however, quite short, and not especially strong. 



The Teeth. 

 The teeth of Claosaurtcs are confined entirely to the maxil- 

 lary and dentary bones. In each, the teeth are very numerous, 

 and are arranged in vertical series, so that they succeed each 

 other as the functional teeth are worn away. This is seen in 

 Plate Y, figures 1-3, which show the form of the teeth and 

 their relations to each other in the same series. The number 

 of teeth in each series depends upon the position, those near 

 the middle of the jaw having the greatest number, sometimes 

 six or more. The teeth of the upper jaw have the external 

 face of the crown covered with enamel and ridged. In the 

 lower jaw, this is reversed, the ridged face of the crown being 

 on the inside. This arrangement greatly increased the cutting 

 power of the jaws. The food was probably soft vegetation.* 



*In describing the skull and teeth of Hadrosaurus, an allied form, Cope made 

 many serious errors, among them the following: the predentary bone is mis- 

 taken for the dentary, the dentary is regarded as the surangular and as the sple- 

 nial, while the squamosal is called the parietal. (Proc. Phil. Acad., 1883, p. 91, 

 plates vi-vii.) Another mistake in the same paper is the statement that the name 

 Attantosauridw was given in 1882. It was given by the writer in 1877. See this 

 Journal, vol. xiv, p. 514. 



