52 . ANATOMY 



The height of the skull was determined by measuring a perpendicular 

 distance between the greatest convexity of the parietal bone in the me- 

 dian line and the junction line between the basi-occipital and the basi- 

 sphenoidal bones on the ventral surface. 



The cranial capacity: The skull was held vertically, with the nose 

 downwards and was filled with fine shot (no. 11) to the upper level of 

 foramen magnum and then the nose of the skull gently struck twice 

 against the palm of the hand. 



Although this is a simple procedure yet it needs the greatest care to 

 produce uniform results. By practice Hatai has been able to reduce 

 the difference between the first and second filling to less than one per 

 cent. The cranial capacity thus determined in the terms of shot weight 

 can be transformed into brain weight as follows : by dividing the weight 

 of the shot in the case of the males by 5.980 and in the case of the females 

 by 6.009. Tables 16 and 17. 



The greatest difference found between the measurements of 

 the skulls for the two sexes is in the nasal bones, which are 

 nearly 2 per cent longer in the male skull. The greater relative 

 length of the nasal bones in the male may be regarded as a sec- 

 ondary sexual character (Hatai). 



Teeth. Addison and Appleton ('15) report as follows on the 

 size and growth of the incisor teeth in the Albino. 



The dental formula of the rat is 



T 1 r P M 3 



l l S) F M 3 



There is only one set of teeth, and hence the dentition is mono- 

 phyodont. The time of eruption of the various teeth extends 

 over a period of 3| weeks. The incisors are the first to appear, 

 viz., at 8 to 10 days after birth. The first and second molars 

 erupt at about the 19th and 21st days respectively, and it is 

 after this latter period that the young animals may be weaned 

 and are able to maintain an independent existence, as far as 

 food is concerned. The third molars are delayed until two 

 weeks later and do not appear until about the 35th day. 



Owing to the lack of precise data, no exact comparison can 

 be made with the eruption of the corresponding teeth in man. 

 Nevertheless, the incisors and the first and second molars in 

 the deciduous dentition of man do erupt at about the equivalent 

 ages (i.e. thirty times the age in the rat) while the relation of 



