358 CLASS XVI. 



development of the brain is obvious from the position of its several 

 parts which are no longer situated in one plane, behind each other, 

 as in fishes and reptiles. The broad medalJa oblongata now makes 

 an obtuse angle with the spinal marroAV of the neck. The second 

 cerebral mass, which in fishes and reptiles is situated in front of 

 the cereheUnm and behind the hemispheres of the cerebrum (see 

 above, p. 4.'i), is here placed below, and on the upper surface are 

 seen the two large hemispheres and the cerebellum alone. This 

 last, although it has lateral appendages, still consists principally of 

 the middle ])art, which in anatomy is named vermis cerehelli. The 

 medulla of the cerebellum presents that peculiar branching expan- 

 sion to which the name of arbor vitte is given in human anatomy. 

 The cavity of the medulla oblongata (the fourth ventricle) pene- 

 trates far into the cerebellum. On the sm-face of this medullary mass 

 many transverse furrows are visible. The cerebrum exhibits no 

 convolutions, but has an entirely smooth surface; it has capacious 

 cavities {ventriculi laterales) in which large striated eminences are 

 seen [corpora striata). Above and behind the anterior commissure 

 is a thin transverse medullary lamina, which, according to the inter- 

 esting discovery of A, Meckel, connects, as a rudimental corpus 

 callosum, the two hemispheres^ On the base of the brain no pons 

 Varolii is yet visible (p. 227); in front of the medulla oblongata 

 the under surface of the above-named second cerebral mass is seen 

 as two lateral eminences corresponding to the corpora quadrigemina 

 and hollow internally. From these the very thick optic nerves 

 proceed forwards, form a curve and approach each other transversely 

 to meet in front of the infundihidum where they split into a number 

 of medullary laminae, which receive one another on each side like 

 the fingers of two clasped hands. The olfactory nerves arise from a 

 conical swelling at the fore part of the hemispheres ; white medul- 

 lary fibres at the base of the hemispheres run in part to these 

 nerves ; those fibres may be followed in the other direction as far 

 as the optic thalami. The pairs of cerebral nerves are the same in 



^ Compare especially A. Meckel Anaiomie des Gehirns der Vogel in J. F. Meckel's 

 Archiv filr die Physiol, ii. 1816, s. 25—78, Tab. I. Many figures of the brain of 

 birds are to be found in the first edition of Wagner's Icones Physiolocjiae, Tab. 22, 

 figs. 2, 3, 4, Tab. 23, figs. 14—17, Tab. 24, fig. 16, Tab. 25, fig. 9, Tab. 26, fig. 5, 

 Tab. 37, fig. 13. 



