FOSSIL MAMMALIA. 79 



The basilar process of the occipital bone is perforated at its middle by two 

 small foramina (i) on the same transverse line, about half an inch apart. 



In the Armadillo these foramina do not exist : in the Orycterope they are 

 present, but open beneath an overhanging ridge, which is continued from them to 

 the upper part of the anterior condyloid foramen on each side. The sella turcica 

 of the Orycterope is deeper and narrower than in the Scelidothere; and is separated 

 from the basilar occipital process by a transverse ridge, which sends forward two 

 short clinoid processes ; two smaller anterior clinoid processes project backwards 

 from the angle of the anterior boundary of the sella turcica. The foramina ovalia 

 and rotunda open in the same continuous groove, as in the Glossothere and Sceli- 

 dothere, but they are relatively wider apart ; and the canal for the third division 

 of the fifth pair is shorter, and runs more directly outwards. 



The petrous bone in the Scelidothere is relatively larger than in the Glossothere, 

 but this probably arises from the precocious development of the organ of hearing 

 in the present immature specimen in obedience to the general law. The trunk of 

 the fifth pair of nerves does not impress it with so deep and well defined a groove 

 as in the Glossothere; the elliptic internal auditory foramen (k) is situated about 

 the middle of the posterior surface ; behind this is the aqueductus vestibuli ; and 

 immediately posterior to the petrous bone is the foramen jugulare(Z) : the shape of 

 the os petrosum agrees more with that of the Armadillo than with that of the 

 Orycterope. An accidental fracture of the right os petrosum demonstrates its 

 usual dense and brittle texture, and at the same time has exposed the cochlea with 

 part of its delicate and beautiful lamina spiralis. The conservation of parts of 

 the organs of vision in certain fossils, has given rise to arguments which prove that 

 the laws of light were the same at remote epochs of the earth's history as now i 

 and the structures I have just mentioned, in like manner, demonstrate that the 

 laws of acoustics have not changed, and that the extinct giants of a former race of 

 quadrupeds were endowed with the same exquisite mechanism for appreciating 

 the vibrations of sound as their existing congeners enjoy at the present day. 



The brain, being regulated in its development by laws analogous to those which 

 govern the early perfection of the organ of hearing, appears to have been relatively 

 larger in the Scelidothere than in the Glossothere : it was certainly relatively 

 longer ; the fractured cranium gives us six inches of the antero-posterior diameter 

 of the brain, but the analogy of the Orycterope would lead to the inference that it 

 extended further into the part which is broken away. The greatest transverse 

 diameter of the cranial cavity is four inches eight lines : these dimensions, 

 however, are sufficient to show that the brain was of very small relative size in the 

 Scelidothere; and, both in this respect, and in the relative position of its principal 

 masses, the brain of the extinct Edental closely accords with the general character of 

 this organ in the existing species of the same Order. We perceive by the obtuse 



