I2l6 



HUMAN ANATOMY. 



from the supraorbital notch, and parallel to the longitudinal fissure to within 18 

 mm. ( y^ in. ) of the fissure of Rolando. The inferior frontal sulcus is represented, 

 approximately, by the anterior end of the temporal ridge. 



In the parietal lobe the most important sulcus is the intraparietal. It begins 

 near the horizontal limb of the fissure of Sylvius, and passes upward and backward 

 about midway between the fissure of Rolando and the parietal eminence. It then 

 turns backward, running about midway to the longitudinal fissure and the centre 

 of the parietal eminence. Above the sulcus, in front, lies the ascending parietal 

 convolution, just posterior to the fissure of Rolando and behind the superior pari- 

 etal lobule. Below the sulcus, anteriorly, is the supramarginal convolution, and 

 posteriorly, the angular gyrus. 



FIG. 1045. 



Eregma 



Lateral ventricle 



Middle meningeal 



rtery, anterior 

 branch 



Posterior horn of 

 lateral ventricle 



(I) Inion 



Lateral sinus 



Middle meningeal artery, posterior 

 branch ; inferior horn or lateral 

 ventricle seen beneath 



Semidiagrammatic view of head, showing position of ventricles, lateral sinus and middle meningeal arteries 



as projected on skull. 



The temporal lobe lies below the fissure of Sylvius and extends forward as far as 

 the edge of the malar bone. The first temporal sulcus lies about one inch below and 

 parallel with the fissure of Sylvius, and the second about 18 mm. (3/ in.) lower. 



The occipital lobe lies posterior to the parieto-occipital fissure and the tem- 

 poral lobe. 



The motor tracts are made up of the fibres passing from the motor portion of 

 the cortex in the Rolandic region to the motor nuclei from which arise the nerves 

 supplying the muscles which the cortical areas control. After leaving the cortex the 

 fibres pass downward in the corona radiata, and converge to the posterior limb of the 

 internal capsule. The motor fibres of the cortico-bulbar and cortico-spinal tracts, 

 occupy the genu and adjacent third of the internal capsule (page 1188), although 

 Drjrrine holds that the whole posterior limb is motor. They continue their course 

 downward through the crura cerebri, pons, and medulla ; in the lower part of the 

 latter the greater number cross to the opposite side and pass down in the cord as the 

 lateral or crossed pyramidal tract. A small number, sometimes absent, pass down 



