NERVOUS SYSTEM. VERTEBRATA. 207 



Metatherian hippocampus. The Rabbits hippocampus is 



restricted to the caudal part of the ventricle and does not 

 extend so far forward as that of the Wallaby (D. 210). 



Note the continuity of the lateral ventricle with the 

 cavity in the olfactory bulb. 



D. 265. Two casts of the cranial cavity of a Rabbit (Lepus cuni- 

 eulus).. 



OHDEII CHIROPTERA. 



D. 266. A cast of the cranial cavity of a Rotisette Bat (Pteropus 

 campynis). 



The brain in the Chiroptera exhibits features which 

 indicate its lowly status in the mammalian series. It does 

 not show signs of any marked specialisation or divergence 

 from the primitive type of the Insectivora. 



The hemisphere is peculiar in that the rhinal fissure is 

 almost completely deficient, although the well-developed 

 pyriform lobe and neopallium present typical features. In 

 the small bats the minute cerebral hemispheres are separated 

 by a wide gap from the cerebellum so that almost the whole 

 of the corpora quadrigemina is exposed. These hemispheres 

 are, of course, quite smooth. In the larger forms, such as 

 Cynonycteris, there is a well-developed splenial complex of 

 calcarine and intercalary sulci of the typical form. In the 

 largest representatives, such as Pteropus, this splenial arc 

 becomes even more extensive. 



On the cranial surface there is in Cynonycteris a very 

 short, deep suprasylvian sulcus and a small shallow lateral 

 sulcus. The latter may in some cases become deeper and 

 more extensive. In this cranial cast of Pteropus there 

 is a short, deep, suprasylvian and a short, shallow, lateral 

 sulcus. 



There is no orbital sulcus, nor is there any trace of a 

 pseudosylvian sulcus. 



In the larger Bats the cerebral commissures are well- 

 developed and resemble those of Galeopithecus. But in 

 many of the smallest Bats (e. g. Nyctopliilus and Vespertilio) 

 the corpus callosum becomes extremely reduced in size so 



