274 Medulla Qttongata. [Book IX. 



Thefe ramifications unite to form a medullary trunk; 

 the middle, anterior, and mod confiderable part of 

 which forms two procefles, the crura cerebelli, which 

 uniting with the crnra cerebri conflitute the medulla 

 oblongata, which will be riext defcribed ; when the 

 cerebellum is cut horizontally this appearance is entirely 

 loft. 



The medulla oblongata is fituated in the lower and 

 pofterior part of the cranium, and is formed of two 

 confiderable medullary procefles of the cerebellum, and 

 of the two larger procefles of the cerebrum called their 

 crura. It may therefore be confidered as a medullary 

 mafs common to both cerebrum and cerebellum, by 

 rhe reciprocal continuity of their fubftances through 

 the great notch in the tranfverfe ftptum. The me- 

 dulla oblongata can only be feen when removed from 

 the cranium, and the description can only apply to the 

 parts when viewed in their inverted fituation. 



.The crura cerebri arife from the middle and lower 

 jfort of each hemifphere. Where they arife from the 

 cerebrum they are feparate, but converge as they run 

 backwards fo as to refe'mble the letter V. Where they 

 unite they form a middle tranfverfe protuberance called 

 the pons Varolii, becaufe th&t anatomift compared it 

 to a bridge, and the two crura cerebri to two rivers. 

 This ccmparifon, however, conveys no idea of the real 

 appearance of the parts, and the pons Varolii is to be 

 confidered merely as an* eminence formed by the union 

 of the crura of the cerebrum and cerebellum. 



Between the crura cerebri and near the anterior edge 

 of the pons Varolii are two white eminences, named 

 eminentise mamillares. From tht pofterior part of 

 the pons Varolii the medulla oblongata is contracted, 

 and defcends obliquely backwards to the foramen 

 magnum of the os occipitis, where it terminates in the 

 a medulla 



