252 A MANUAL OF ANATOMY. 



The floor of the fourth ventricle is the widely separ- 

 ated internal surface of the pons and medulla. It is tra- 

 versed along the median line by a fissure the posterior 

 median sulcus. 



Parallel with the anterior half, and on either side of the 

 posterior median sulcus, is a rounded ridge the fasciculus 

 teres which is produced by the fibres of the facial nerve. 



A small depression is in the lateral recess opposite the 

 posterior part of the eminentia teres, the fovea superior, 

 and in front of this depression is a small bluish spot, the 

 locus cseruleus. 



Some transverse fibres are seen crossing the floor of the 

 ventricle just behind the lateral recesses ; these are a part 

 of the auditory nerve and are named the striae acusticse. 

 They cross a little elevation, which is the tuberculum acus- 

 ticum. Behind this tubercle is a second shallow depres- 

 sion, which is the fovea inferior. Extending backward 

 and inward from the inferior fovea is the ala cinerea, a 

 dark area over the nuclei of the ninth and tenth nerves. 



The ventricle narrows to a pointed extremity the cala- 

 mus scriptorius which is contained within the clavae of 

 the funiculi graciles. 



Internal to the ala cinerea is another small elevation, the 

 trig-onum hypoglossi, which is over the nucleus for that 

 nerve. 



The Posterior and Lateral Surfaces of the Medulla. 

 Back of the fourth ventricle the sides of the medulla come 

 together, the space between them being called the poste- 

 rior median fissure. 



By the anterior and posterior median fissures the medulla 

 is divided into two lateral halves ; each half of the medulla 

 is further subdivided by the antero- and posterolateral 



