G. T. BETTANY ON THE GENUS MERYCOCBXEKUS. 265 



crest from a single specimen of M. temporalis, where it is almost 

 perfectly preserved on the right side. I have thought it best to 

 describe the temporal fossa and its boundaries fully here, instead of 

 leaving it for the subsequent description of the species. 



The long axis of the temporal fossa is directed forwards and out- 

 wards at an angle of about 40° with the middle line. Its extreme 

 length could not have been less than eight inches in M. temporalis : 

 but this cannot be exactly determined, because the upper and pos- 

 terior boundary is almost entirely broken off. But it may be stated, 

 to give some idea of its size, that, notwithstanding the high develop- 

 ment of the face and nasal cavities, the temporal fossa is larger than 

 the face. It is bounded behind by the transverse occipital crest, 

 thus extending almost to the extreme posterior limit of the skull. 

 This boundary was continued by the anterior of the forks into 

 which that crest divides, running outwards and somewhat forwards. 

 The height of this crest cannot be determined ; but it appears pro- 

 bable that it was not less than an inch high. The external angle 

 of the temporal fossa, situated midway on its lateral aspect, is 

 occupied by the great posterior transversely-placed zygomatic crest. 

 The crest slopes away in front so as to leave no external boundary 

 to the fossa. Internally the fossa was bounded by the high sagittal 

 crest, which appears to have continued at the same level as the 

 frontal surface, or very little lower than it. The bifurcation of the 

 sagittal crest forms the antero-internal wall of the fossa, which was 

 in front limited by the posterior orbital arch. 



The whole internal surface of the temporal fossa is very smooth, 

 and gently and beautifully curved. The lateral wall of the cranium, 

 which may be said to constitute the internal floor of the fossa, is 

 convex, and is formed almost equally by the squamous and the 

 parietal bones. Their suture is along the line of the most marked 

 prominence of the convexity, and lies midway between the middle 

 line and the outer boundary of the fossa. This prominence, together 

 with a slighter ridge above it and parallel with it, constitutes a 

 rather broad shallow groove. I would suggest that this ridge marks 

 the limit separating the upper and anterior from the lower and 

 posterior portion of the origin of the temporal muscle. Near the 

 posterior termination of this ridge, which is on the parietal, and 

 between it and the squamous suture, is a large foramen which Dr. 

 Leidy identifies as venous. There is in our specimens a smaller 

 foramen just behind and below this. 



The internal lateral boundary and floor of the fossa in its middle 

 portion presents, from above downwards : — first, a considerable con- 

 cavity formed by the nearly vertical rise of the sagittal ridge ; 

 secondly, the convexity on the side wall of the cranium ; and, lastly, 

 another deep but gently curved concavity directed downwards, for- 

 wards, and outwards along the inside of the posterior and external 

 ridge, which extends forwards from the occipital crest. 



The extreme depth of the fossa depends on the height of the 

 sagittal ridge ; but it was at any rate equal to two thirds of the 

 total length of the fossa. 



