JURASSIC VERTEBRATE FOSSILS. 



499 



seen in the sacrum, when- there is a very large chamber formed by an 

 enlargement of the spinal canal. This chamber is ovate in form, and 

 strongly resembles the brain-case in the skull, although very much larger, 



Fig. 52.— Skull of &A s Marsh; side view. One-fourth natural size. 



a, anterior narial open in ower temporal fossa d, dentarj ; fp t post- 



frontal; j mal ; m, masillarj ; n, naaal; oe t occipital condyle; pd, predentary; pf, prefrontal; pm, premax- 



illary; po, postorbital; q t quadrate s aplenial; sa, surangular; so, supraorbital; «g, squamosal, 



d 



i . -Tooth of >''< ■■ 



/>. outer view . ■■ ■ p view. 



ice Datura] i 



FlG. 54.— Brain-cast of Stegosaurus ungulatt t . side view. 



'-. cerebral hemispheres m, medulla; oJ, olfactory lob< - 



''.ist of neural cavity in sacrum of Siegosaurtu ungulatus; side view. 

 a, anterior end ; /, foramen between first and second vertebras ; / ,same between sei 

 ■n third anil last vertebra ; p, exit of neural canal in last sacral vertebra. 

 Both figures are one-fourth oatui i 



"/' optic lobes 



being at least twenty times the size of the cavity which contains the brain. 

 This large, vaulted chamber is mainly contained in the first and second 

 sacral vertebrae, although the canal is considerably enlarged behind this 



