190 LECTURE VII. 



and fifteenth year. This is followed by a rapid transformation 

 in the forms and proportions of the skeleton. The transforma- 

 tion proceeds difierently in the cranium and the face ; the jaws 

 predominate without an adequate compensation in the cranium. 

 It is not meant that there is exactly an arrest of development ; 

 but that the race difference consists in the different growth of 

 individual parts. Whilst in the white man the gradual increase 

 of the jaws and the facial bones is not only equalled but ex- 

 ceeded by the development or rather enlargement of the brain, 

 and specially of the anterior lobes ; the reverse is the case in 

 the Negro. The muscles subservient to animal life cause a 

 compression on the sides, which is but little resisted by the 

 brain. In this way the cranium obtains the shape previously 

 described. As everything in the organism is harmonious, this 

 theory of cranial formation may be contested, but the mode in 

 which the sutures close furnishes an important commentary on 

 these phenomena. The central frontal suture closes in the 

 Negro in early youth, as well as the parietal part of the coronal 

 suture.* With advancing age the central portion of the coro- 

 nal suture, the saggital suture, and all parietal sutures close, 

 nearly simultaneously, as I have observed in skulls from East 

 Africa. The lambdoid suture remains open the longest, speci- 

 ally at the apex. At the base of the cranium we find, on the 

 contrary, the suture between the sphenoid and the occipital 

 bone stih open, and the suture between the incisors is not 

 only seen in the Negro child, but in many old Negro skulls. 

 Generally speaking, the sutures in the Negress close sooner 

 than in the Negro. 



"Prognathism may, perhaps, be partly considered as the result 

 of the action of the lower jaw on the concentric arch of the upper 

 jaw. At any rate, the mode of its direction towards the temporal 

 bone contributes to it ; for I have found this formation princi- 

 pally in races where the sockets for the lower jaw are broad 

 and less deep, whilst the heads are flat or at least elliptical. 

 This agrees with a greater or lesser harmony of the rows of 



* In the numerous skulls I have examined, there occurred but a single 

 exception. The progress of the closure of the sutures seems to me to ditter 

 generally according to the form of the long or short skulls. 



