Miscellaneous . 301 



bone. As lu-urapophyses tlie prelrontals here lend their whole ex- 

 tent to the snpport of' their neural spine — the nasal hone, which is 

 divided, like the frontal antl parietal, by a median suture. The large 

 size of both pre- and post-frontals relates to the large size of the eye, 

 and of the cavity destined to contain it. 



The nasals are the longest and largest bones of the cranium ; 

 departing, in this respect, widely from the cetacean type, and re- 

 taining that of the Labyrinthodout and Crocodilian skulls. They 

 send a pointed process backwards into a corresponding notch of the 

 frontal to close contiguity with the ])ari('tals, and they receive in 

 shallower notches the anterior bifurcations of the frontal. The outer 

 angle of the pouter notch touches the post- frontal. By the outer 

 border the nasals successively unite with the prefrontal, lacrymal, 

 maxillary and premaxillary, their junction with the former being 

 concealed by the overlapping hind end of the premaxillary ; between 

 the lacrymal and maxillary intervenes the nostril, the upper border 

 of which is formed by the nasal. 



The palatines are long slender bones commencing behind, between 

 the pterygoid and ectojjterygoid, forming the inner boundary of the 

 small palatal nostril ; continuing, mesially, in articulation with the 

 pterygoids, until these diminish to a point, then touching each other 

 at the median line, and united externally to the maxillary and jjre- 

 maxillary : the palatal plates of the latter underlap the palatines. 



The maxillary commences behind, under the bent styliform jugal, 

 opposite the anterior third of the orbit ; as it advances it expands 

 into a palatine and alveolar plate, articulating internally with the 

 ectopterygoid, forming part of the outer boundary of the naso- 

 palatine aperture, and then uniting with the palatine bone and with 

 the palatal ])late of the premaxillary. The palato-alveolar part of 

 the maxillary is divided from the facial part by the well-developed 

 external alveolar wall. The facial part, coming into view beneath 

 the fore-part of the malar bone and of the orbit, expands vertically 

 as it unites with the lacrymal to form the lower boundary of the 

 external nostril ; in advance of this the maxillary becomes over- 

 lapped by the premaxillary, which gradually covers it from view at 

 about the fifteenth tooth, in Ich. tenuirostris, counting forwards, 

 but the maxillary extends further forwards, after it is so overlapped. 

 As a general rule, it supports about one-third of the dental series of 

 its own side of the jaw. In Crocodiles the maxillaries support, gene- 

 rally, three-fourths of the dental series, and their relative size to the 

 premaxillaries is greater in Lizards. Fishes present the nearest re- 

 semblance to the Ichthyosaurs in regard to the small share which 

 the maxillaries contribute to the formation of the dentigerous mar- 

 gin of the upper jaw. 



The j)remaxillaries, on the other hand, present in the Ichthyo- 

 saurus as peculiar a degree of superior magnitude ; a difference due 

 not so much to the prolonged form of the snout which obtains in 

 Crocodilia, as to the disproportionate shortness of the maxillary 

 bones; 



Each long premaxillary begins, behind, by an expanded and deeply 



