158 Annals of the Carnegie Museum. 



no accessory facets on the basi-occipitals for the atlas. The foramen 

 magnum is of fairly large size and its general outline is heart-shaped. 

 The paroccipital process is subject to considerable variations within 

 the species. In the type this process is compressed antero-posteriorly, 

 has broad anterior and posterior surfaces, is well separated from the 

 occipital condyle, and is closely appressed to the postero-external 

 part of the tympanic bulla. Sometimes this process is more trihedral. 

 The basi-occipital is not very broad, and on the inferior surface there 

 is a strong keel in the median line. The condylar foramen is of moder- 

 ately large size and is located nearer to the tympanic bulla than to the 

 condyle. The basicranial axis is gently curved. 



Though the sagittal crest is very prominent, the parietal region as a 

 whole has a rather small area anteio-posteriorly as well as laterally. 

 This is due to the small size of the brain-cavity, which is a character- 

 istic feature. The upper contour of the cranium is somewhat similar 

 to that in Coloreodon ferox Cope, while the downward sweep of the 

 zygomatic arch somewhat suggests that of the Entelodonts. The 

 heavy zygomatic arch, with its rugose surfaces, has given rise to 

 considerable speculation with regard to its function. It has been 

 suggested that it supported weapons of defense,^ but the present Avriter 

 is more inclined to think that it provided attachments and support 

 for muscles. The temporal and zygomatic fossa? in this species are 

 certainly very capacious, due chiefly to the abnormal transverse spread 

 of the zygomatic arch, and it is very evident that there was also a 

 heavy masseter muscle which had a small antero-posterior extent and 

 consequently required an extra heavy and rugose surface for its apo- 

 neurotic attachments. The zygomatic arches of the pigs are generally 

 quite heav}^ and when careful comparison is made between the species 

 under description and the recent form Potamochosrus chceropotamus 

 it is seen that the zygomatic arch in the latter, though different in 

 position and shape, is proportionally as heavy as in the fossil species 

 and is also quite rugose, especially in fully adult specimens. The 

 width of the sagittal crest in Promerycoclnvrus carrikeri is variable in 

 different individuals, which perhaps is a sexual character. This 

 broad transverse area is especially noticeable on the skull of the skele- 

 ton No. 1078 of the group mounted and on exhibition in the museum. 

 This skeleton is regarded as that of a male. The glenoid cavity 

 presents a large transverse and antero-posterior surface, which is 



8 Douglass, E., Bull. Amer. Mus. Nat. Hist., Vol. XXIII, p. 118, 1907. 



