R. S. Lull — Cranial Musculature in Dinosaurs. 391 



to the occipital bones, of which the dorsal and ventral ones were 

 powerful, the lateral ones relatively feeble. 



Just above the foramen magnum in the supraoccipital bone 

 lie two deep depressions separated by a thin lamina of bone. 

 These are continuous with a median groove on the ventral sur- 

 face of the parietal extending backward about two-thirds of the 

 distance toward the margin of the frill. Along the center of 

 this groove lies a slight ridge running backward for about half 

 its distance, the precise extent being variable. This ridge is 

 continuous with the lamina which divides the depressions in 

 the supraoccipital. In .the two specimens of Triceratops 

 serratus the parietal groove fades out toward the rear, while in 

 T.jyrorsus it ends abruptly and is quite deep at the posterior 

 end. Just beneath this groove when the cervical s are in situ 

 lie the neural spines of the second, third, and fourth vertebree, 

 which are depressed backward so as to lie nearly parallel with 

 the under surface of the frill. There can be no question that 

 we have here the insertion on the skull of the complexus major 

 muscles, which arose from the cervical spines and expanded 

 upward and forward in a pair of relatively thin sheets as in 

 the chameleon. These muscles were of prime importance, not 

 alone in fulfilling the function of the ligamentum michw of 

 the mammal, but also from a developmental standpoint, as will 

 ultimately be shown. They served to maintain the poise of 

 the skull and were probably, as in recent reptiles, continua- 

 tions of the longissimi dorsi which run the length of the back. 

 At the extremities of the exoccipitals and upon the adjacent 

 ventral surfaces of the squamosal bones are large, depressed 

 muscle areas which were confluent. These, if taken collec- 

 tively, were the insertions of the largest muscle masses of the 

 neck, those which, lying as they did in the wake of the supra- 

 orbital horns, bore the brunt of the strain, in wielding these 

 powerful weapons {vide infra, p. 395). It is somewmat difficult 

 to homologize these muscles with accuracy but they must have 

 included the comjplexus minor, the anterior prolongation of 

 the latissimus dorsi, the insertion of which is normally in the 

 exoccipital. The under surface of the frill shows other some- 

 what variable depressions, notably in the parietal bone near 

 the squamosal suture. These are well out toward the periphery 

 of the frill (Plate III). I am not sure of their identity, but it 

 is reasonable to suppose that the whole neck of the creature 

 must have been enormously muscular, covering the entire 

 lower surface of the frill except for its free margin, the extent 

 of which is a specific variation). 



From the frequency with which one observes injuries, per- 

 forations and fractures, upon the ceratopsian skull, 1 cannot 

 believe that the powerful armament of the horns was for mere 



