544 



THE NEEVOUS SYSTEM. 



Frenului 



Anterior medullary 

 velum 



Brachium con- 

 junct! vum 



Brachium pontis 



Striae medullares 

 Area acustica 



Ala cinerea 

 (trigonum vagi) 



Puniculus cuneatus 

 Funiculus gracilis 



Tsenia thalani 



Pineal body 



Superior quadri- 

 geininal body 



Inferior quadri- 

 geminal body 



Pedunculus cerebri 



Pontine part of floor 

 of 4th ventricle 



Colliculus facialis 

 Fovea superior 



Restiform body 



Trigonum 

 n. hypoglossi 



Clava 



Tuberculum 

 cihereum 



Funiculus cuneatus 



is carried upwards to the lower border of the pons, but is often rendered ven 

 shallow by numerous external arcuate fibres which emerge upon the surfac< 



between its lips am 

 then curve laterally t< 

 reach the posterior par 

 of the medulla oblon 

 gata. At the lowe 

 margin of the pons i 

 expands slightly am 

 ends in a blind pit 

 which receives the nam 

 of the foramen caecur 



The fissura median 

 posterior is present onl 

 on the lower half of th 

 medulla oblongata. A 

 it ascends it rapidl 

 becomes shallowei 

 Half-way up, where th 

 central canal opens int 

 the fourth ventricli 

 the lips of the posteric 

 median fissure are thrus 

 apart from each oth( 

 and constitute theboui 

 FIG. 479. POSTERIOR .VIEW OF THE MEDULLA, PONS, AND MESENCEPHALON daries of a trianuulc 



OF A FULL-TIME HUMAN FOETUS. c 1 J "U 1. 



field, which is seen whe 



the epithelial roof of the lower part of the fourth ventricle is removed. This tr 

 angular field is the lower part of the fossa rhomboidea, or the floor of the fourt 

 ventricle of the brain. The lower half of the medulla oblongata, containing as it dot 

 the continuation of the central canal of the spinal medulla, is frequently terme 

 the closed part of the medulla oblongata ; the upper half, above the opening of tl 

 canal, which contains the lower part of the fourth ventricle, is called the opt 

 part of the medulla oblongata. 



The examination of the floor of the fourth ventricle will be deferred for tl 

 present, and the appearance presented by the surface of the medulla oblonga 

 may now engage our attention. In the spinal medulla the corresponding surfa< 

 area is divided into three districts or funiculi by the emerging motor roots and tl 

 entering sensory roots of the spinal nerves. Of these the sensory enter aloi 

 the bottom of the sulcus lateralis posterior, whilst the motor fila are spre* 

 over a relatively broad surface area and have no groove in connexion with the 

 emergence from the spinal medulla. In the case of the medulla oblonga 

 corresponding rows of fila enter and emerge from the surface of each side. The fi 

 of the hypoglossal nerve carry up the line of the anterior nerve-roots of the spin 

 medulla. In one respect, however, they differ : they emerge in linear order ai 

 along the bottom of a distinct furrow, termed the sulcus lateralis anterior, whi< 

 proceeds upwards on the surface of the medulla oblongata. The fila which car 

 up the line of the posterior nerve-roots on the 'surface of the medulla oblonga 

 are the root-bundles of the accessory, the glosso-pharyngeal, and the vagus nerv- 

 These are attached along the bottom of a furrow which is the direct continuati 

 upwards of the sulcus lateralis posterior of the spinal medulla, and therefc 

 receives the name of the sulcus lateralis posterior of the medulla oblongata. T 

 root-bundles of these nerves differ, however, in so far that they are not all compos 

 of afferent fibres which spring from ganglionic cells placed without and enter t 

 medulla. Certain of them are purely efferent (roots of accessory), whilst oth< 

 contain a considerable number of efferent as well as afferent fibres, and are the: 

 fore to be regarded as mixed roots. 



By the sulci laterales, and also by the two rows of fila attached along t) 



