THE MEDULLA. OBLONGATA. 351 



they then diverge, and advance forwards and upwards to ter- 

 minate above in the cerebellum. 



The corpus restiforme is formed of medullary matter, and is 

 a continuation of the posterior chord of the medulla spfpalis. 

 From its superior posterior margin a thin medullary lamina of 

 about three lines square arises, and being sustained by the pia 

 mater, advances to meet its fellow, but does not absolutely touch 

 it.* From the anterior margin of each corpus restiforme there 

 departs a second process of medullary matter, larger and more 

 thick than the preceding, and being covered by the roots of the 

 pneumogastric and glosso-pharyngeal nerves, adheres to the 

 plexus Choroides of the fourth ventricle. 



The superior face of the medulla obiongata is excavated be- 

 tween the corpora restiformia, in such a way as to present the 

 outline of a writing pen, and is, therefore, called Calamus 

 Scriptorius; which forms a considerable part of the floor of the 

 fourth ventricle of the Brain, or the sinus rhomboideus. The 

 fissure, in its middle, corresponds with the slit of a pen, the 

 nib being downwards; and the fissure extends from the poste- 

 rior fissure of the medulla spinalis the whole length of the me- 

 dulla oblongata. 



The calamus scriptorius is marked by several streaks of me- 

 dullary matter, which extend themselves transversely with a 

 very slight degree of obliquity upwards, and reach the external 

 margin of the corpus restiforme of the corresponding side. 

 These medullary strice present some varieties in regard to their 

 volume, number, and arrangement. Sometimes they are slightly 

 elevated narrow lines, which are perfectly distinct from each 

 other, and from one to fourteen in number. On other occa- 

 sions their volume is greater, but they are not so numerous. 

 They generally extend, either one or all, from the middle fis- 

 sure to the commencement of the auditory nerve, and are 

 thereby a part of its origin- Sometimes the anterior ones are 

 directed towards the origin of the trigeminus nerve, but their 

 union with it is not yet ascertained; the posterior ones are some- 

 times blended with the radical filaments of the pneumogastric 

 nerve. The striae themselves, are sometimes interwoven or 

 blended, and pass the boundary of the middle fissure to join 



* Called Pons Sinus Rhomboidei by J. F. Meckel. 



