6 FOSSIL REPTILIA OF THE 



The longitudinal depression (fig. 6, d) is bounded below by the angular 

 element, or part answering to that marked 2 in Pterodactylus suevicus, and 

 above by the sur-angular (c). This element appears to have coalesced with the 

 articular one ; but between the bone (a, c) and that marked b a true harmonia or 

 toothless suture remains. The line below the letter e , in fig. 6, appears to be an 

 accidental crack. The fractured anterior end of the fragment (fig. 10) indicates 

 the extreme thinness of the wall of the bone, which consists of compact osseous 

 substance. A part of the concave, articular, surface is shown at a, fig. 7. 



A similar longitudinal depression on the inner side of the back part of the 

 ramus, with its lower boundary produced as a ridge, and formed by the angular 

 element (2), is indicated in the figure of the lower jaw of the Pterodactylus 

 luevicus in Professor Quenstedt's memoir; according to the proportions of 

 which jaw, the present comparatively enormous fragment would answer to almost 

 the hinder half of that part of the ramus which has not united with its fellow 

 to form the long symphysis, and it may be estimated as including one fourth of 

 the entire length of the lower jaw, which would give to the Pterodactyle, yielding 

 the present mandibular fragment, a head exceeding sixteen inches in length. It 

 is probable, however, that the head of Pterodactylus simus was relatively 

 shorter and thicker than in the smaller species of Pterodactyle. 



The Basi-occipital (Tab. I, figs. 11, 12, 13). 



A skull of the size above indicated would require an occipital condyle at least 

 as large as that on the basi-occipital element figured in the above-cited plate. 

 This condyle projects backward on a well-marked base too broad to be called a 

 peduncle ; the convexity is only hemispheric, with the transverse diameter pre- 

 dominating; its shape and position indicate great freedom of movement of the 

 head upon the spine. There is no mark of a sutural surface for the exoccipitals on 

 the expanded part of the bone (b) ; they were probably confluent, as in birds, with 

 the basi-occipital, and have been broken away; the fractured surface (fig. 12, b) 

 shows the large cancelli of this part of the occipital bone. The upper surface ( a ) 

 indicates a wider foramen magnum, or neural canal, than that of the combined 

 atlas and axis (fig. 14, «), and such a structure accords with the free and exten- 

 sive movements of the head upon the spine indicated by the form and promi- 

 nence of the condyle and its occipital cup ( c ). 



Atlas and Axis (Tab. I, figs. 14, 15, and 16). 



The anchylosed atlas and axis (figs. 14, 15, and 16) correspond in size with the 

 above-described basi-occipital ; they were obtained at the same time from the 



