568 



3413. The separated bones of the skull of a new-born or very young Hippopotamus 

 amphibius. 



The deciduous incisors and canines and the summits of the first three deciduous molars, 

 p 1, d2 and d3, have protruded in both jaws: those of the fourth (last) deciduous molar 

 had just begun to pierce the gum in the lower jaw, but had not emerged from the formative 

 socket in the upper jaw. The germs of the permanent incisors and canines and of the first 

 true molars (m 1) had begun to be calcified. In the premaxillary there is a smooth deep 

 fossa at the back part of the interspace between the two deciduous incisors, which may have 

 contained either the germ of a third incisor, or of a successional incisor. 



In the upper jaw the first, p 1, and second, d 2, deciduous molars have simple conical 

 crowns : the third, d 3, has four cusps, the two hindmost being on the same transverse 

 line : the fourth, d 4, has four cusps in two transverse pairs, like the permanent molars. In 

 the lower jaw the first, p 1, and second, d 2, deciduous molars have conical crowns : the third, 

 d 3, has two principal cusps, the second being bifurcate, answering to the pair of cusps in the 

 broader tooth above : it has also an anterior basal talon, answering to the first cusp of the 

 corresponding tooth above, and a very small posterior talon : the fourth milk-grinder, d 4, 

 has three pairs of cusps, with an anterior and posterior talon. The tooth here described as 

 the first deciduous molar is less advanced in its development than d 2 and d 3, and, as it has 

 no vertical successor, it may be regarded as the first premolar, p \. The basioccipital has 

 partially coalesced with the basisphenoid, but not with the exoccipitals ; it forms no part of the 

 occipital condyles, and developes no processes from its under surface : its lateral synchondrosal 

 surfaces are divided into two facets, one for the part of the exoccipital behind the precondyloid 

 foramen, the other for the smaller part in front. These parts of the exoccipital have not 

 coalesced on the inner side of that foramen, which is single : the exoccipital developes, besides 

 the condyloid process, the paroccipital and a broad process to join the mastoid. The super- 

 occipital is a thick, rhomboid, vertical plate. The alisphenoids have coalesced with the basi- 

 sphenoid : they are short, and are grooved behind by the boundary which they contribute to 

 the foramen common to the foramen ovale and the basicranial foramen lacerum, and more 

 deeply in front by the part they contribute to the foramen common to the foramen rotundum 

 and foramen lacerum anterius : they develope long pterygoid processes, which are imperforate, 

 and articulate along their inner sides with the entopterygoids. The presphenoid has coalesced 

 with the orbitosphenoids and with the rudimental prefrontals, which are connate, compressed, 

 and form the median septum of the great anterior outlet of the cranial cavity. The vomer is 

 a long, slender, pointed bone, deeply grooved above. The parietals articulate with the ali- 

 sphenoids, orbitosphenoids, squamosals, inastoids, frontals, superoccipital, and each other. 

 The under part of the frontal is divided into a cranial, orbital and olfactory surface ; the 

 orbital surface being the largest, and the superorbital ridge broad and much produced. The 

 petrosal, mastoid, tympanic and squamosal elements of the temporal have coalesced. The 

 meatus internus is a deep fossa divided into a cribriform surface below and a canal above : 

 the tympanic swells into a large three-sided conical protuberance below. The palatines pro- 

 long the bony palate beyond the series of grinding teeth in use. The symphysis of the lower 

 jaw is not obliterated. 



Presented by Prof. Owen, F.R.S. 



