CHAP. XVI.] 



SOME OTHER MAMMALS. 



261 



liarities of the several parts of the Brain, as met with in 

 different representatives of the great class of Quadrupeds. 



The Medulla, the Cerebellum, and the pons Varolii, 

 are so intimately related to one another, hoth struc- 

 turally and functionally, that they may here he regarded 

 as constituting one compound division of the Brain. 



There is nothing special to he said concerning the 

 Medulla in Quadrupeds, except that 

 the lateral projections, known as ' oli- 

 vary bodies,' gradually become more 

 developed (fig. 72, v). In many ani- 

 mals, a layer of fibres on each side, 

 known as the * corpus trapezoideum ' 

 (fig. 73), crosses these structures and 

 partially hides them. In higher Quad- 

 rupeds, however, such transverse fibres 

 cross the Medulla at a higher level or 

 appear to be absent (fig. 74). Where 

 this is the case the ' olivary bodies ' are 

 uncovered ; and as they also become 

 larger, they may form rounded promi- FIG. 73. Brain of Rabbit, 

 nences, one on each side of the Medulla, under surface^ (Soiiy after 



' ^ Leuret.) A, Olfactory lobe ; 



The above-mentioned ' corpora trape- 1, Lobe of the Hippocampus, 

 zoidea,' usually cross the Medulla at the 



level of the * origin ' of the auditory and occuii; c , corpus mammii- 



/, . , m , , . , . lare ; p c, eras cerebri ; p v, 



tacial nerves. They are very distinct P0 ns varom ; 6 , corpus tra- 

 in the Lion, the Dog, and the Sheep.* P ezoideum ; *. ***** 



* pyramid ; c r, olivary body. 



The upper part of the Medulla is 



bridged above and closely embraced by a much thicker 

 mass of fibres known as the pons Varolii, the develop- 

 ment of which in different Mammals, is found to be strictly 

 proportionate to the development of the lateral lobes of 

 the Cerebellum. 



* See Tiedemann's ' Icones Cerebri Simiarum,' Tab. m. and vn. 



