134 Mammalia. 



Three well marked Convolutions belong to this lobe : two of them 

 are vertical in direction, and are separated from each other by the 

 Pissure of Rolando ; these are, (.) the anterior of the two, the First 

 Ascending Convolution, [h.) the Second Ascending convolution : {c) 

 the third is the Curved Convolution, which winds round the superior 

 extremity of the Parallel Fissure : this Convolution has an as- 

 cending branch, and a descending branch which is continuous with 

 the Middle Temporal Convolution. 



3. Temporo-sphenoidal Lobe, This lobe lies below the Fissure of 

 Sylvius. It embraces three Convolutions, which are usually oblique 

 in direction ; they are 



a. Superior Temporal. l. Middle Temporal. c. Inferior Tem- 

 poral. 



The superior and middle convolutions are separated from each 

 other by the Parallel Fissure, around the summit of which winds the 

 Curved Convolution. 



4. Occipital Lohe. The convolutions in this lobe are three in 

 number, and take a longitudinal direction. They are 



a. Superior Occipital. h. Middle Occipital. c. Inferior Occipi- 

 tal. 



The anterior border of the Occipital lobe often, as here, is thin, 

 and projects forward over the external perpendicular fissure : it is 

 then called the * Operculum.' 



There are moreover on the external surface four Bridging Convo- 

 lutions, two of which are of considerable classificatory importance ; 

 mz. those which connect the Parietal lobe with the Occipital. 



The first passes from the posterior extremity of the Second Ascend- 

 ing Convolution to the Superior Occipital Convolution. The second 

 passes from the summit of the descending branch of the Curved Con- 

 volution to the Superior Occipital. The third external Bridging Con- 

 volution connects the Middle Temporal with the Middle Occipital j 

 the fourth connects it with the Inferior Occipital Convolution. The 

 two latter are always superficial. The others are sometimes super- 

 ficially, sometimes deeply placed. 



B. Internal Surface. 



About the middle of the Internal Surface is seen the Great 

 Central Aperture, round which the Convolutions are ranged and 

 through which the Crus Cerebi passes upwards. It is divided into 



