100 PKOF. OWEN ON EOSSIL EVIDENCES 



4. On Fossil Evidences of a Sirenian Mammal (Eotherium cegypti- 

 acum, Owen) from the Nummulitic Eocene of the Mokattam 

 Cliffs, near Cairo. By Prof. Owen, C.B., P.R.S., F.G.S., &c. 

 (Head November 18, 1874.) 



[Plate III.] 



The evidence of the Sirenian mammal now submitted to the Society- 

 is from the white, compact, fine-grained, calcareous stone of the 

 JNummulitic Eocene Tertiary period, now quarried extensively in the 

 Mokattam cliffs, south of Cairo, for the buildings in progress in the 

 modern part of that city. 



The block of stone containing the fossil was shown and after- 

 wards presented to me by Dr. Grant, an eminent practitioner in 

 Cairo, who possesses a good illustrative collection of fossil shells 

 from the above formation ; but the appearances of the exposed parts 

 of the present fossil were, as may well be supposed, both new and 

 strange. That the block contained the cast of some organic cavity 

 was the best interpretation I could, at first sight, offer ; and the 

 subsequent clearing away of the matrix determined the fossil to be 

 part of the cranium, with a cast of its interior representing the 

 brain, of a species of Sirenian mammal. 



The portions of the skull preserved are scanty ; they include 

 parts of the basioccipital, basisphenoid, and petrosals. The bodies 

 of the two cranial vertebrse have not coalesced, but show the flat, 

 vertical, roughish syndesmotic surface, which long remains in the 

 recent Dugongs* and Manatees f. The alisphenoids are confluent 

 with the basisphenoid; and the line of union is impressed, on the 

 inner or cranial surface, by the large trigeminal nerve. 



These portions of cranial bones have the dense texture character- 

 istic of the Sirenian skeleton. The petrosals, of a deeper tint, show 

 an almost crystalline fracture, yielding at least a compact polished 

 surface. The preserved part of the basioccipital is the fore one, where 

 it gains vertical thickness, with a small part of the hind flatter por- 

 tion, the rest being broken away from the expansion to join the con- 

 dyloid parts of the exoccipital ; so much as remains shows the extent 

 of the free lateral surface contributing to the large vacuity in the cra- 

 nial walls, in which the petrotympanic bones are loosely suspended. 



The cast, as finally worked out, includes the entire brain and the 

 beginning of the myelon (Plate III. figs. 1-4). This cast bears about 

 the same proportion to that of the cranial cavity of the existing 

 Manatee (fig. 5) as does the cast of the cranial cavity of the Anoplo- 

 there % to the brain of a modern ruminant of the same size as that ex- 



* See Home, Phil. Trans. 1820, p. 154, pi. xiii. fig. 1. 



t Vrolik, Bijdragen tot de natuur. &c, Kermis van den Manatus americanus 

 (fol., 1852), vierde Plaat, fig. 12, b, c. 



\ Cuvier, ' Ossemens Fossiles,' torn. iii. (4to, 1822), pi. vii. fig. 3, p. 44. E. 

 Lartet, " De quelques cas de progression organique verifiables dans la succession 

 des temps geologiques sur des mammi feres de meme famille et de meme genre." — 

 ' Comptes Rendus de l'Acad. des Sciences,' Paris, l er Juin, 



