82 THE CEEATOPSIA. 



part of a third tooth. These present the characters of the genus Diclonius and of either the species D. calamarius or D. 

 ferangulatus, or one not described. 



These bones exhibit anomalous characters and with one exception their identification presents a difficult problem. They 

 were numbered in the order of their discovery from I to 12, but I commence the description with No. 8, as the one which 

 furnishes the basis for the determination of the others. This portion of the skull includes the united occipital and sphenoid 

 regions, with some lateral elements in close contact with them. The sutures separating the basioccipital and basisphenoid, 

 the exoccipital and prootic, and the prootic and basisphenoid are distinct and squamosal in character. Other sutures are 

 not visible. The bones are generally thin, especially their superficial dense layer. 



A remarkable peculiarity of the basal axis of the cranium is its obliquely ascending direction, as its plane makes with 

 that of the posterior occipital surface an angle of 40°. The latter plane was also directed forward, as indicated by the posi- 

 tion of the occipital condyle, so that the posterior portion of the skull rose like the abutment of an arch from the vertebral 

 column. This structure also contracts the space occupied by the brain, a deficiency which is compensated by its elongation 

 forward. 



The basioccipital is, in its axial portion, exceedingly short, the condyle and its peduncle including two-thirds of its length. 

 [n front of this is a considerable expansion, consisting of two huge cup-shaped postero-inferior processes, which spread out 

 laterally and inferiorly from the neck of the condyle, partially concealing it from an inferior view. They are separated by a 

 deep emargination immediately below the condyle. These processes are doubtless the insertions of powerful muscles and 

 appear to be homologous with those found on each side of the basis cranii anterior to the occipital condyle in the emeu. 

 Their borders are separated from those of the exoceipitals by a deep notch on each side. This element may be the true 

 sphenoid, although sutural distinction from the basioccipital is not clear. [See fig. 4, A, B, and C, this monograph.] 



The exoceipitals have an aliform lateral expansion, which extends beyond the lateral walls of the brain case. Each one 

 consists of two principal ribs, which terminate in projections which are separated by a concave thin margin. The anterior is 

 curved forward. The posterior is straighter and is directed outward and a little backward. The supraoccipital is narrow 

 and is bounded by an elevated ridge on each side, which approach each other upward. The postero-superior face is deeply 

 concave and is divided by a strong median carina or crest of the same elevation as the lateral crests. The foramen magnum 

 is relatively large and is a little higher than wide. It is probable that the supraoccipital bone does not form part of its 

 border, although, a very small portion having been broken from its posterior edge, the question is not positively decided. 

 The occipital condyle is relatively large and consists exclusively of the basioccipital bone. It is a portion of a globe, the 

 superior convexity being interrupted by a small plane. It is supported on a short neck, on the superior face of which are 

 two lateral shallow concavities. 



The presphenoid or sphenoid bone is simple and of remarkable length, resembling that of a bird or snake rather than that 

 of a lizard. It has no posterior lateral processes corresponding to those in front of the basioccipital bone, but embraces the 

 base of the former equally all round by a squamosal suture. The notch separating the occipital processes is continued as a 

 wide groove, which rapidly contracts to an acute termination an the posterior part of the basisphenoid bone. It is bounded 

 on each side by an elevated ridge. These are bounded externally by an open groove on each side, which unite farther forward 

 on the basisphenoid. These are in turn bounded on the outer side by an obtuse ridge, which are not continued on the 

 sphenoid. The median portion of the basisphenoid is convex from side to side. The anterior portion is narrower, and the 

 cranial cavity is here strongly compressed. 



Four foramina are situated on the posterior part of the walls of the cranial cavity. These probably represent the fenestra 

 ovalis, the foramen laccrum posterius, and the foramen carotideum. The first named is quite large and perforates the poste- 

 rior part of the exoccipital bone, a part of its posterior border being formed by the crested sphenoid and a small part of its 

 interior lower margin being probably contributed by the basisphenoid. An inferior tongue-like prolongation of the exoc- 

 cipital bone separates it from a large foramen in front of it, which it bounds in conjunction with the presphenoid and prootic. 

 This foramen is oval, with the long axis directed upward. Between it and the fenestra ovalis the exoccipital is pierced by a 

 much smaller round foramen at a, point below the middle of the former. The prootic bone is prolonged forward and at a 

 point much anterior to the exoceipitals, and the remaining part of the supraoccipitals bounds another foramen of not large 

 size. This, perhaps, gave exit to one of the branches of the trigeminus. The anterior extremity of this part of the skull is 

 very peculiar. The sphenoid, from an ascending direction, turns horizontally, while the supraoccipital rises apparently as a 

 median ascending process free from the inferior walls. The latter acquires another roof, which incloses an open cavity with 

 the supraoccipital, which expands forward and has its lateral borders composed of the united produced lateral angles of the 

 inferior and superior bounding Surfaces. The brain chamber turns forward and the superior part of it terminates rather 

 abruptly. The inferior part of the cast of the matrix, which occupies it, is continued with a subtriangular section, resembling 

 the hypophysis or the united peduncles of the olfactory lobes. The roof of this chamber rests on an osseous mass in front, 

 which is concave above from side to side; below, its broken section is transverse, its vertical diameter small and least in the 

 middle. 



There is some uncertainty attending the determination of the elements which compose the mass above described. It is 

 possible, as already observed, that the recurved, cup-shaped basal bone is the sphenoid, and not the basioccipital. This 

 interpretation receives some countenance from those offered in explanation of the few crania of Dinosauria hitherto found. 

 These are two, or perhaps three, viz, one described by Mr. Hulke, and a second by Prof. H. G. Seeley in the Quarterly Jour- 

 nal of the Geological Society of London, and another published near the same time by Doctor Bunzel in the quarto of the 

 K.-K. Mineralogische Anstalt of Vienna. 



In all of these the basicranial axis is deflected immediately in front of the occipital condyle, in Doctor Seeley's specimen 

 to a very great extent, as much as in the Crocodilia of later periods. In the other two crania the deflection is less marked, 



