526 DR. J. MUEIB ON THE ANATOMY OF THE SEA-LION. 



occipital lobule divides the rearmost gyrus, bending round a backward spur of the 

 collateral sulcus to blend with the lower occipital and temporal convolutions. The 

 anterior division of the lobule proceeds by an inflexion to the calcarine gyrus. 

 The collateral sulcus is deep and somewhat X-figured. Its two posterior furrows 

 embrace the lower post-segment of the occipital lobule ; its two anterior similarly 

 enclasp the posteriorly directed calcarine loop, but have a more horizontal plane ; and 

 the lowermost is the longer. The calcarine sulcus is L-shaped : the lower backward 

 limb courses between the calcarine and uncinate gyri ; the upright limb is prolonged be- 

 tween the representatives of the uncinate, the internal occipital, and the callosal lobule. 

 It meets the internal perpendicular fissure above, where a triradiate arrangement of the 

 sulci obtains. What coincides with the calcarine gyrus is a prolongation of the extremity 

 of the lower anterior limb of the occipital lobule. This fold, at fii'st with a slight 

 anterior bend, turns horizontally backwards, and again curves forwards in a parallel line 

 below — that is, forms a loop becoming without division, or is continuous with the 

 uncinate gyrus. This latter convolution widens somewhat in front, and sends up and 

 round the cerebral crus the fold agreeing with the uncinate lobule. A well-defined dentate 

 sulcus runs between the crus and the fore border of the dentate lobule. The upper 

 border of the latter gyrus is in proximity to the duplicature of the callosal lobule, whilst 

 a narrow wedge or horn slants upon the splenial knee of the corpus callosum. 



f. Folds and Furrows, left half of the Cerebrum. — I intimated there being a certain 

 amount of asymmetrj' on the two sides of the brain ; and fig. 38 partially displays that 

 want of harmony in the furrows and ridges With regard to the outer face of the left 

 hemisphere, the more prominent and characteristic gyri and fissures as described on the 

 right segment also obtain, the variations depending on minor duplications and incisions. 

 For example, the Syhian fissure has its perpendicular and oblique posteriorly directed one ; 

 but the latter divaricates at the angular and posttemporal lobules and mounts towards 

 the occiput, forming an island or separated fold of that between the external perpen- 

 dicular fissures. Again, the mid-temporal gyrus seems to have a second division, or, 

 rather, the anterior V-shaped knuckle of the posttemporal constitutes a descending 

 isthmus alongside, and rivals the mid-temporal in size. The mid-frontal gyri are less 

 sulcated ; but the superofrontal has fully more indents and superficial sculpturing, 

 rather than clearly defined induplications of gyi'us. The lobule of the supramarginal 

 convolution is fuller, the first vertical sulcus above and behind being insulated, the 

 seconji deepened and, as it were, taking the place of the first. The anteroparietal 

 gyrus has imperfect continuity with the postparietal at its commencement ; but the 

 great longitudinal y'-shaped fissure of Eolando clearly separates them above, as on the 

 right half. The suprafrontal has a well-marked duplicature or loop where it joins the 

 anteroparietal at the great marginal gyrus. The anteroparietal presents behind a 

 trifurcate arrow-headed wedge ; and instead of a single continuous loop with outward 

 turn to the internal perpendicular fissure, two longitudinal but obliquely directed folds 

 connect it ^vith the termination of postparietal and angular gyri. 



