118 



ANATOJklY OF VERTEBRATES. 



^■^^ 



i -V\^'-j 



pehdc one is greatest in most otlier birds, 

 and especially in the Cursores. The alar 

 enlargement is due to an accession of 

 white and grey substance, without dila- 

 tation of the myelonal canal. 



In the brain of a chick at the eighth 

 day of incubation, fig. 39, the 'fourth 

 ventricle ' is exposed by divergence of 



39 



Brain of emhryo Bh"d. 



Brain of Lizard, ccxvi. 



the dorsal myelonal columns which noAv 

 have the name of ' posterior pyramids :' 

 the plate of neurine developed from them 

 to bridge over the ventricle shows the 

 same incipient state of the cerebellum, ib. 

 b, as in the Batrachia : it next expands 

 at the middle and represents the condi- 

 tion of the cerebellum in the Lizard, fig. 

 40 : continuing to grow, the cerebellum, 

 fig. 41, e, covers, at the sixteenth day of 

 incubation, the fourth ventricle, and has a 

 smooth exterior, as in the Crocodile and 

 Turtle (vol. i. fig. 191). Towards the 



Brain of chick at IC days. Id. at 20 days, ccxvi. 

 MyelenceplialoD, or brain and spinal cloSC of iuCubatioU tllC CCrebellum, fig. 



42, c, presses forward toward the cere- 



chord, with part of the backbone, of a 

 bird (Anser) 



