SKULL AND BRAIN IN MAN. 259 



The greater curvature of the human skull is the fun- 

 damental condition of that enormous additional space afforded 

 for the human brain, and also for the relatively abundant 

 space provided for the nasal, oral, and pharyngeal cavities. 



We must associate the diminution of the spheno-basilar 

 angle, and the elimination of the palato-occipital angle, with 

 the increased depth of the cerebellar fossre, with the horizon- 

 tality of the tentorium, and with the extension backwards, 

 and vaulted form of the parietal region of the cranium, for the 

 reception of the posterior lobes of the cerebrum. 



Again we must associate the elimination of the spheno- 

 ethmoidal angle, and the diminution of another angle, the 

 vomerine (to be alluded to in the sequel), with the horizon- 

 tality of the cribriform plate, and of the orbital plates of the 

 frontal with which that plate is connected, as well as with 

 the vaulted form of the frontal itself ; and, consequently, with 

 the great increase in the mass and complexity of the anterior 

 lobes of the human cerebrum. The same peculiarities secure 

 for man the inferior position, and horizontal arrangement, of 

 the nasal chambers, orbits, and oral cavity. 



The antero-posterior and transverse curvatures of the vault 

 of the skull, as well as the curvatures of the fossa3 on the floor 

 of the cranial cavity, are anatomically conditioned by the sur- 

 face curvatures of the respective lobes of the cerebrum and 

 cerebellum. The mass and form of the entire brain is the 

 condition which determines the volume and curvature of the 

 several compartments of the cavity which contains it, while 

 the required mass of the entire organ is the condition which 

 d (ermines the permanence of the primordial form of antero- 



berior curvatures. 



/. The vomerine angle La the angle between the lower 

 a pect of the sphenoid, and the posterior margin of the vomi r. 

 Ii is least in man, and increases as we descend the series of 

 the mammals. Tin- character of this angle is the primary con- 



