The Anatomy of Chlamydoselachus 



353 



In Chlamydoselachus, any consideration of the cranium as a whole must take into 

 account its relation to the upper jaw (palatoquadrate) and to the suspensory apparatus, 

 on both of which it seems, to a considerable degree, to be molded. As one looks at the 

 skull from the side (Figure 5, plate II) he is impressed by the extraordinary length of the 

 jaws which begin posteriorly far behind the cranium and lie, when the mouth is closed, 

 in a nearly horizontal position. The ectethmoidal process projects over the outer surface 

 of the palatoquadrate, thus helping to hold it in place. The postorbital process of Chlamy- 

 doselachus is exceptionally large, but even when the mouth is closed it fails to reach the 



c'a. 



c. 



octv. 



Text-figure 23. 

 Inner view of the right half of the skull of Wexanchui to show the cranial portion of 



the notochord and the foramina for cranial nerves, 

 ac., foramen for auditory nerve; a.p., antorbital process; c, carotid foramen; ca., interorbital canal; gp., 

 glossopharyngeal nerve; m., membrane over fontanelle; -ac, notochord; o., optic nerve; ocn., spino-occipital 

 nerve; om., oculomotor nerve; r., rostrum; tg., trigeminal nerve; Vr., trochlear nerve; Dg., vagus nerve; 



vs., occipitospinal nerve. 

 From Goodrich, 1909, Fig. 93, after Gegenbaur, 1872. 



palatoquadrate. The nearly terminal position of the mouth is attained somewhat at 

 the expense of the cranium, for the rostrum is short and thin, though broad, and the 

 anterior third of the ventral surface of the cranium slants upward in such a way as 

 to allow the anterior part of the upper jaw to lie on a level with the posterior part of 

 the basis cranii. This is only one of several adjustments that make this creature, when 

 viewed from in front with its enormous jaws spread apart (Text-figure 2), seem to be 

 nearly all mouth. When this same specimen with the wide-open mouth is viewed from 

 the side, it appears that, m the process of opening the mouth, the upper jaw (and of 

 course, the cranium also) is elevated anteriorly, thus keeping the center of the mouth 

 cavity in line with the body. The site of this flexure is not in the occipi to-vertebral 

 articulation, but in the vertebral column a few centimeters posterior to it. How this 

 flexion is accomplished I do not know, since the vertebral column has no articulations 



