I500 A MANUAL OF ANATOMY 



The nerve-fibres issue from the ventral aspect of the nucleus, and 

 the nerve-funiculi pass through the medulla oblongata in a dorso- 

 ventral direction, lying between its anterior and lateral areas, and 

 between the formatio reticularis alba and formatio reticularis 

 grisea. Having reached the bottom of the ventro -lateral sulcus 

 between the pyramid and the olive, they emerge from the medulla 

 oblongata in line with the sixth cranial nerve superiorly. 



The two hypoglossal nuclei, right and left, are connected with 

 each other by commissural dendrons; and each nucleus receives 

 collaterals from the pyramidal tract of the opposite side, being 

 thereby brought into connection with the pre-Rolandic motor area 

 ot the opposite cerebral hemisphere. 



Distribution. — ^The hypoglossal nerve is the motor nerve of the 

 tongue, and supplies (i) the stylo-glossus, (2) the hyo-glossus, 

 (3) the genio-hyo-glossus, and (4) the intrinsic muscles of the tongue. 



Cranio-cerebral Topography. 



The auricular point is the centre of the orifice of the meatus 

 auditorius externus. 



The pre-auricular point is situated in the depression between the 

 tragus of the auricle and the condyle of the mandible. 



The bregma, or point of junction of the sagittal and coronal 

 sutures, corresponds to the centre of a line connecting the two 

 auricular points (the centre of the orifice of the meatus auditorius 

 externus) . 



The lambda, or meeting of the sagittal and lambdoidal sutures, 

 is situated about 2f inches above the inion, or external occipital 

 protuberance. 



The pterion, or region of the spheno-parietal suture, is situated 

 about I J inches behind the external angular process of the frontal 

 bone, and about if inches above the zygomatic arch. 



The asterion, or point where the parieto-mastoid, occipito- 

 mastoid, and lambdoid sutures meet, is situated about 2 inches 

 behind the auricular point, very nearly in line with the upper 

 border of the zygomatic arch. 



The sagittal line represents the line which connects the nasion, 

 or meeting of the two fronto-nasal sutures, with the inion. 



The sagittal suture corresponds to that part of the sagittal line 

 which extends from the lambda to the bregma. 



The coronal suture is indicated on either side by a line extending 

 from the bregma to the pterion. 



The lambdoid suture (occipito-parietal) corresponds to a line 

 extending from the lambda to the asterion. 



The squamo-parietal suture, and its continuation backwards as 

 the parieto-mastoid suture, are indicated by a curved line, with 

 the convexity upwards, extending from the pterion to the asterion, 

 ■ the highest part of the curve being about 2 inches above the zygo- 

 matic arch. 



