892 MR. R. W. PALMER ON THE 



cannot be determined, owing to the continuity of their casts Avith 

 those of the tiunsverse sinuses. 



Such a primitive foi'm of cerebellum in an organ of this size is 

 unknown, except in Marsupialia [llacropios and Thylacinas) [6J. 



Brain-stem. 



In cranial casts this region is never represented with any 

 accvu'acy, owing to the fact that the nerves and vascvilar spaces, 

 which lie below the brain, obscure the outlines of the latter. 



Conspicuously shown (text-fig. 156, p. 887) to the outside of the 

 pituitary region are the courses of the nerves escaping by the 

 sphenoidal fissure (which, as mentioned above, is confluent with 

 the foi'amen rotundum) and by the foramen ovale. 



The course of the trigeminal nerve can be followed from the 

 outside of the region of the Pons Varolii, along a groove in the 

 alisphenoid to the foramen ovale, through which it gave off its 

 mandibular branch, and then, still lying in a groove on the bone, 

 the second and first branches ran forward to pierce the skull with 

 the third, fourth, and sixth nerves through the sphenoidal fissure. 

 Occupying the centre of the figure formed by these two pairs of 

 f oraminal casts, the pituitary body is represented, but the extreme 

 shallowness of its fossa makes it very inconspicuous. The pos- 

 teiior clinoid processes leave a scarcely noticeable impression on 

 the plaster. 



As to the divisions of the rest of the brain-stem nothing can 

 be distinguished. It only i-emains to describe the casts of the 

 periotic region, of the foramina for the veins of the sinus, and 

 of the last cranial nerves. 



The periotic bone has left an irregular cratei'-like scar on the side 

 of the cast (text-fig. 155, p. 886). This hollow is walled by various 

 nodose elevations, which are chiefly casts of parts of the tiansverse 

 sinus. In the centre of the "crater" a tiny ridge represents the 

 passage through the internal auditory meatus and the Aqueductus 

 Fallopii of the Ylllth and Vllth nerves. The upper boundary 

 of the crater is formed by the cast of the floccular fossa. In 

 front and below is the cast of the foramen lacerum medium, 

 from which a slight ridge runs forward on the base of the brain 

 to meet its fellow of the other side below the pituitary fossa. 

 This ridge may have some connection with the course of the 

 internal carotid. Below and at the back of the periotic depres- 

 sion, an elevation represents the foramen lacerum posterius. At 

 the back of the floccular lobe of the cerebellum, a tiny knob marks 

 the position of the mastoid foramen (text-fig. 156, tn.f.). 



On the side of the medulla oblongata, in line with the jugxilar 

 foramen, the exit of the Xllth nerve is represented by a tubeicle 

 which is the last feature to be seen on the cast. 



At this point a summary of the resemblances between the 

 brains of Orycteropus and Anojjlotherium may not be out of 

 place. The Aard-Vark's brain has been described as differing 

 from a primitive Ungulate type only in a higher development of 

 the olfactory parts. The only other important contiust with the 



