170 Mammalia, 



On pressing tlie Cerebellum backwards so as to gain a view 

 of tbe parts intervening between tbe Cerebrum and Cerebel- 

 lum, the following structures will be disclosed. At tbe 

 posterior margin of tbe Corpus Callosum there will be seen in 

 tbe median line tbe posterior extremity of the Velum Inter- 

 posifum, a vascular membrane reflected from the Pia Mater into 

 the interior of the Brain. The Velum will be seen to pass 

 beneath the posterior rounded border of the Corpus Callosum, 

 and above the Corpora Quadrigemina : on slightly raising 

 Hs posterior border it will be found to form an almost complete 

 investment for a small conical reddish body, which rests upon, 

 or rather in, the division between the anterior pair (nates) of 

 Corpora Quadrigemina. This conical reddish body is the 

 Pineal Gland (Conarium) so named from its peculiar shape 

 (pinus, the fruit of the fir) ; in its base, as we shall afterwards 

 see, is a small cavity communicating with that of the third 

 ventricle. Posteriorly to these are the Corpora Quadrigemina 

 (optic lobes) ; four rounded eminences, separated by a crucial 

 depression ; the anterior larger pair are called JSfates, the 

 posterior pair the Testes : they will be found to be situated 

 immediately behind the third ventricle : and are seen to be 

 connected with the Cerebellum by means of a large white cord 

 on each side, the processus a cerehello ad testes, or * superior ' * 

 peduncles of the Cerebellum ; stretched between these two 

 peduncles will be seen a thin translucent lamina of medullary 

 substance, called the Valve of Vieussens ; it covers-in the 

 canal leading from the third to the fourth ventricle {iter a 

 tertio ad quartum ventriculum) and forms part of the roof of 

 the latter cavity: from the upper part of the valve, im- 

 mediately behind the testes, arises the fourth or trochlear 

 nerve, as above mentioned. 



Examination of the Interior of the Brain. 



* Cf. supra. Restiform bodies. 



