MONOCLONIUS RECUEVICORNIS. 83 



and it terminates in an angle, from which the axis continues forward. In Mr. Hulke's specimen it rises somewhat, as in the 

 Montana animal. In none of the crania is the element in front of the condyle recurved as in the latter, though they display- 

 in their angle a rudiment of the prominent crest above described. In none of the European crania is the supraoccipital region 

 directed obliquely forward, as in the Diclonius, but the lateral constriction is seen in Doctor Seeley's specimen. 



It is then possible that the bone which I have called a downward prolongation of the exoccipital is the prootic, although 

 I can not certainly detect any suture separating it from the former. In that case the large foramen in front of it becomes the 

 foramen ovale, the bone in front of it the alisphenoid, and the anterior foramen the foramen opticum. In view of the form of 

 the brain this identification is not without probability. 



The cast of the brain does not display any median fissures. Its vertical depth is greatest a little anterior to the foramen 

 magnum, where it is compressed, the sides being shallowly concave and separated from the superior surface by a longitudinal 

 angle. In front of this position it is subcylindric and the anterior extremity comes to an obtuse termination, which is con- 

 vex in cross section and concave in the vertical sense, the lower portion continuing downward and forward, possibly to the 

 hypophysis. 



Before describing the remaining cranial bones the significance of the characters above recorded may be considered. As 

 regards the form of the brain, the superior elevation of the posterior region above the anterior is a point of resemblance to 

 birds rather than to reptiles. The apparent absence of prolongation of the hemispheres into the olfactory lobes is also a char- 

 acter of birds rather than of reptiles. The brain cavity is in fact closed in front above, as in Mr. Hulke's skull already men- 

 tioned, which also presents no prolongation for the olfactory lobes. This is present even in those reptiles where the chamber 

 is closed in front — e. g. , Ophidia — while it is absent in birds. When viewed from above there are other affinities indicated. 

 The absence of indication of lateral optic lobes points to reptiles and not to birds, while the small diameter of the hemispheres 

 is not like either class, but resembles more the state of things in Batrachia and fishes. The characters of the osseous structure 

 present some avian affinities. Such are the simple semiglobular occipital condyle, the infero-posterior processes of the basi- 

 occipital, and the short, thin, lateral processes of the exoccipital bones. The great prolongation of the basisphenoid, the lack 

 of lateral processes of that bone, and the absence of overhanging lateral margin of the superior cranial walls may be looked 

 upon as ophidian or avian characters. Lacertilian characters are completely wanting. The anterior termination of the brain 

 case and its basis resembles nothing else. 



In close contact with the side of the mass above described was found a bone of peculiar form, which doubtless belongs to 

 the suspensorium. There could be no doubt of this were the bone suturally united with the cranial element proper. It is, 

 however, only applied to it by the intervention of a body of hardened matrix, of the peculiar color of that which occupies the 

 cranial chamber and which differs much from the lignite in which I found the bones embedded. Almost in contact I found a 

 corresponding piece of the opposite side of the skull, but with a more extensive attachment of an adjoining bone. I therefore 

 describe this bone in preference to the first named. It consists of two bones, one a tabular mass, the other a projecting body 

 resembling a horn core, standing on one of the extremities of the table and at right angles to its plane. The tabular part of the 

 bone is thick, and its free border (opposite to the horn-like bone) is excavated, so as to be double. The two plates are con- 

 nected by crosspieces, which inclose three fossa?. Both the marginal and inferior faces of the bone display smooth surfaces, as 

 though for synovial articulations. The external surface is roughened with tubercles. The horn-like bone rises from the prob- 

 ably exterior border of the tabular bone, which embraces part of its base in a fixed articulation. It is a rather short and stout 

 cone, with a subtriangular section, much rounded on the inner side. The apex is rather abruptly contracted from the inner and 

 from what I suppose to be the superior sides. Its base is continuous with that of the tabular bone, and terminates externally — 

 i. e., on the side away from the tabular bone — in a thick projecting rim. The surface of the horn-like portion is deeply grooved 

 and scored, probably for nutritive vessels, as the grooves are continuous. The texture of these bones is for some distance dense, 

 but is more spongy in the center. The corresponding bone of the opposite side does not differ from it. 



These bones are evidently lateral; but little can be asserted as to their true nature. The position in which one of them 

 was found would lend support to the view that 'they are the united opisthotic and squamosal, or either of those bones plus the 

 quadrate. Certain it is that none of those bones are attached suturally to the posterior part of the cranium in this animal, in 

 which it differs from all other reptiles. The infero-anterior surface of the exoccipital resembles much more that of the same 

 region in birds, and the proximal faces in the anomalous bones described are of similarly smooth character. One result is cer- 

 tainly derived from this examination, viz, that the Dinosauria (if this genus belong to that order) do not pertain to the divi- 

 sion of Reptilia with fixed os quadratum. This is a realization of an anticipation published in 1870 in the following words: 

 "Those (Reptilia) which consolidate the periotic elements, but retain the partial freedom of the quadrate, on the other hand, 

 lead to the avian class. These are the Ornithosauria and, perhaps, when we come to know the cranium, the Dinosauria. At 

 least this may be predicted if the structure of the foot and ear bones are correlated in this group as they are elsewhere." It is 

 probable that the horn-like processes were directed forward, and also, if the position in which the attached one was found be 

 normal, in a line extending below that of the sphenoid. This position would relate it to the quadrate. This subject may be 

 considered in connection with the. structure of the mandible, discussed further on. 



The next bones, marked as Nos. 1 and 2 in my notes, are from the median line of the skull, and of very peculiai' form. 

 They were found in contact, but it is very doubtful whether the relation they present to each other is the normal one. No. 1 is 

 an L-shaped bone, the short limb of the L being recurved, and with the extremity pointing nearly in the direction of the longer 

 limb. The region at the junction of the L is the thickest, being very massive and solid, and the limbs contract regularly to 

 their extremities. The shorter limb becomes compressed toward the end. The longer narrows more gradually and is convex 

 transversely on the face next the shorter limb. The other face of the long limb exhibits two longitudinal excavations, separated 

 by a vertical septum. The opposite face of the short limb is transversely truncate. The posterior part of the inferior face of 

 the long limb is also flat, and joins that of the short limb at a transverse solid angle, which is a little less thamright. In profile 



