162 Mammalia. 



Looking at the upper surface of the Brain (i.e. that surface 

 on which the convolutions chiefly appear) it will be noted 

 that {a) the large lobes of the Cerebrum do not cover the 

 posterior twisted nodule or Cerebellum, in other words the^os- 

 terior lobe of the Cerebrum of Man is absent (i.e. that lobe which, 

 in Man, rests upon the tentorium and whose extent forwards 

 is limited by the anterior margin of the Cerebellum) ; (b) the 

 Cerebellum does not consist of two distinct lateral lobes con- 

 nected by an elevated median portion, as in Man ; but, rather, 

 the median lobe holds the chief position. 



Looking at the under surface or base of the Brain the student 

 should note, (a) the large size of the Olfactory bulbs on either 

 side of the anterior lobes of the Cerebrum ; (b) the very slight 

 extent to which the so-called ' middle ' lobe appears, owing 

 to the great development of the lobe of the Hippocampus 

 immediately internal to and underlying it; (c) the small 

 size of the Pons ; and (d) the broad Medulla Oblongata. The 

 structures in the median area, and the nerves, will be noted 

 after the removal of the Pia Mater. 



Dissection of PRiNciPAt Arteries. The student should 

 now proceed to follow out the principal trunks of the Arteries 

 that supply the Brain with blood ; viz. the Vertebral and 

 Internal Carotid Arteries. It may be well to be reminded of 

 the course of these vessels after leaving the heart. 



In all Ruminants, both right and left subclavian arteries, 

 and both * common' carotids, arise from one arteria innominata 

 springing from the arch of the Aorta. 



Each Vertebral artery is generally the first branch of the 

 Subclavian of its own side ; it passes through the foramina 

 in the transverse processes of the cervical vertebrae from the 

 sixth forwards, and enters the Skull through the Foramen 

 Magnum : it then passes round the medulla oblongata to 

 blend with its fellow in a common trunk at the posterior 

 border of the Pons : the two vertebral arteries united form 



