64 loiHNA]. OF CoMPAK A 1 1\ 1: NK^K()I.()(,^. 



neck. \'entiad to this neck anothej^ local swelling of the 

 wall of the ventricle diverts the ventricle from the meson. 

 \'entra(l to this level the displaced ventricle does not return 

 to its former proximity to the meson. 



The second division of the ventricle is parallel to the 

 dorsal surface of that hemisphere in which it is found. 



Divisions. — For convenience the prosencephalon has been 

 divided into three regions: the basal region, the mantle and 

 the axial region. The basal region is that portion of the 

 base of the prosencephalon which lies between the caudad 

 extremity of the ventrolateral tuber and the olfactory crura. 

 It is histologically distinct from the remainder of the brain. 

 In it nerve cells are either entirely absent or else represented 

 by what Professor Herrick has termed rhinomorphic cells. 

 The outer portion of the remainder of each hemisphere is 

 called the mantle, while the inner portion is called the axial 

 region. Along the mesal, dorsal and caudal portions of the 

 hemisphere the mantle is separated from the axial region by 

 the lateral ventricle. Elsewhere these two regions of the 

 brain are distinguished by histological characteristics. 



THE MANTLE. 



In the mantle the nerve cells are not distributed promis- 

 cuously, but they are aggregated in distinct and constant 

 localities. The brains of several diflerent groups of birds 

 have been examined, and in all cases the above statement 

 has proved correct. More than that; in the prosencephalon of 

 different birds, corresponding areas are supplied with similar 

 cells. In the reptilian brain, according to Prof. C L. Her- 

 rick, this is also true. In his paper on the cerebrum of the 

 Lizard('), Prof. Herrick has called each of these cell clusters 

 a nidulus and that portion of the hemisphere in which the 

 cluster is found, a lobe. He has named each nidulus, and to 

 each lobe he has given the name of the contained nidulus. 



I See " To)iography and Histology of the Brains of Ceitain Reptile^," liy I'lof. C. L. 

 Herrick. Supra p 1^. 



