SKULL OF HESPERORN1B. 11 



6. There is some evidence that the same general law of brain- 

 growth holds good for Birds and Reptiles, from the Cretaceous to the 

 present time. 1 



The concluding suggestion was in part based on facts now published 

 for the first time in the present memoir. 



The Lower Jaws. (Plate I, figures 2-4.) 

 The lower jaws are long and slender, and were thickly set with teeth. 

 The rami were united at the symphysis in front only by ligament, a feature 

 unblown in modern adult birds. There is an imperfect articulation 

 between the splenial and angular elements, which probably admitted of 

 some motion ; and all the other sutures are open, or distinguishable. There 

 was apparently a mandibular foramen. There is a well marked shallow groove 

 on the outer superior margin of each dentary bone, for the reception of the 

 maxillary teeth, when the jaws were closed. (Plate I, figure 3, 6.) The 

 angle of the mandible extends backward but a short distance beyond the 

 articular face for the quadrate, and the extremity is obliquely truncated. 



The following measurements of the skull of Hesperornis regalis are 

 taken mainly from the very perfect specimen figured in Plate I, and 

 recorded as number 1206, in the Geological Catalogue of Yale College 

 Museum. The other dimensions are derived from number 1207, of the 

 same Catalogue, to which reference is made in all the numbers of specimens 

 given in the descriptions that follow : 



Measurements of Skull. (Hesperornis regalis, No. 1206.) 



Length of skull, from occipital condyle to end of premaxillary, 257.0 mm 



Greatest transverse diameter, behind temporal fossae, 61.0 



Least transverse diameter, between temporal fossa?, 30.0 



Greatest transverse diameter, between temporal fossae and orbits, 42.0 



Least transverse diameter, between orbits, 9.0 



Trans verse diameter of premaxillaries, at anterior nares, - . 9.0 



Antero-posterior diameter of anterior nares, 55.0 



'American Journal of Science and Arts, vol. viii, p. 66, July, 1874; and vol. xii, 

 p. 61, July, 1876. 



