FOSSIL MAMMALIA. 



til 



of the zygoma formed by the meeting of the upper and lower facets presents 

 a semicircular curve, extended transversely from the cranium, and directed 

 forwards. 



The anterior extremity is obliquely truncated from below upwards and 

 forwards, and presents a flattened triangular surface indicative of its junction 

 with an os mala? : the space between this extremity and the side of the cranium 

 measures one inch and nine lines across, and thus gives us the thickness of the 

 temporal muscle. The distance from the origin of the zygoma to the occipital 

 plane is relatively greater than in Orycteropus ; Glossotherium is in this respect 

 more similar to Myrmecophaga and Manis. 



The sphenoid bone forms a somewhat smooth protuberance below and behind 

 the base of the zygoma. The tympanic bone is wedged in between this protuberance 

 in front, and the mastoid process behind. The chief peculiarity of the broad 

 mastoid is the regular semicircular cavity at its under part for the articulation 

 of the styloid bone of the tongue. This depression is separated below by a 

 broad rough protuberance from the foramen jugulare, (J", fig. 2, PI. XVI,) which 

 is immediately external to, and slightly in advance of the great foramen con- 

 dyloideum, c. A small rugged portion of the os petrosum separates the jugular 

 from the carotid canal, which arches upwards and directly inwards to the side of 

 the shallow sella turcica, (the external and internal orifices of the carotid canal 

 are shown at g, figs. 2 and 3). The chief protuberance on the basis cranii is a 

 large and rugged one, serving for the attachment of muscles, and due chiefly to 

 the expansion of a great sinus in the body of the sphenoid. This protuberance 

 is separated from the smaller sphenoid protuberance before mentioned by a 

 large groove continued downwards and forwards from the tympanic cavity, and 

 containing the Eustachian tube, which does not traverse a complete osseous 

 canal. Immediately internal to the glenoid cavity is the large orifice of the canal 

 transmitting the third division of the fifth pair of nerves, the principal branch of 

 which endows the tongue with sensibility ; this foramen (h, fig. 2) is rather less 

 than that for the muscular nerve of the tongue. 



The internal surface of the present cranial fragment affords a very satis- 

 factory idea of the size and shape of the brain of the extinct species to which it 

 belongs. It is evident that, as in other Bruta, the cerebellum must have been 

 almost entirely exposed behind the cerebrum ; and that the latter was of small 

 relative size, not exceeding that of the Ass ; and chiefly remarkable, as in the 

 Orycterope, Ant-eater, and Armadillo for the great development of the olfactory 

 ganglia. The antero-posterior extent of the cribriform plate, as exposed in this 

 fragment, is three inches, and the complication of the cethmoid olfactory lamellae 

 which radiate from it into the nasal cavity is equal to that which exists in the 

 smaller Edentata (fig. 3, PI. XVI). The nasal cavity is complicated in Glosso- 



