NERVOUS SYSTEM. VERTEBRATA. 461 



The cerebellar bridge is now complete and two fissures 

 (in addition to the limiting fissure of the floccular ! 

 have now developed. They are the primary fissure (usually 

 called " preclival ") and the secondary fissure (usually 

 called " prepyramidal "). 



In the spinal cord the cervical and lumbar enlargements 

 are now apparent. 0. 0. 1341 c. 



Presented by John Hilton, i 



D. 678. A human foetal brain (of about the same age as the last 

 specimen) lying in situ in the head. A great part of the 

 lateral wall of the left hemisphere has been removed so as 

 to show the corpus striatum, hippocampus and choroid 

 plexus in the lateral ventricle. It also shows the relation 

 of the fossa Sylvii to the corpus striatum. 



Most of the ridges on the mesial wall are the obverse of 

 those post-mortem puckerings called " transitory fissures." 

 The most caudal of them, however, is not of this nature 

 but is the calcar avis produced by the calcarine sulcus. 



0. C. 1341 D. 

 Presented by John Hilton, Esq. 



D. 679. The central nervous system of a slightly older human 

 embryo, dissected to show the lateral ventricles. 



On the right side the whole of the hippocampus is 

 exposed, whereas on the left side it is hidden by the 

 choroid plexus. 



The calcarine sulcus is well shown on the left side. 

 On the base of the hemisphere note the acutely flexed 

 pyriform lobe. 



The cerebellum is now rich in fissures in the mesial 

 region but only a few of them have yet extended laterally. 



0. C. 1341 E. 

 Presented by John Hilton, Esq. 



D. 680. The brain of a later human foetus. The left hemisphere 

 has been separated. 



The posterior part of the Sylvian fissure is now taking 

 form. The superior limiting sulcus of Reil can be dis- 

 tinctly seen. 



L 



