EXPERIMENTAL. 31 



STUDIES OF SKELETAL MEASUREMENTS. 



Prepared bones as a basis for the determination of the size of an 

 animal have several advantages over living weight or any measurement 

 taken on a living animal. They are practically unchanged by tempo- 

 rary unfavorable conditions or sickness ; the adult size is simple to deter- 

 mine, whereas the body weight may be continuously increased by fat after 

 maturity. Bone measurements are more analytical than weights; they 

 can be more accurately measured and in cases of error or doubt may be 

 remeasured at any time. They also offer material for further investiga- 

 tion, should a new theory or new method of comparison appear. 



To ascertain the age at which bones stop growing, skeletons of rab- 

 bits of various ages were compared. Of the sutures destined to close 

 completely, that between the proximal epiphysis and diaphysis of the 

 humerus was found to be the last to close. By a study of this suture 

 in humeri long boiled with "soapine," it was determined that ossifi- 

 cation is completed by the twelfth month. Sexual maturity comes 

 between the fifth and eighth months. To assure completed growth 

 beyond all doubt, the animals were not killed until they were fifteen 

 months old. In a few cases animals that died between twelve and 

 fifteen months have been included, since by their measurements they 

 were well within the range of others in the same fraternity. 



MEASUREMENTS RECORDED. 



From every animal the long bones of the right fore and hind legs 

 and the skull were cleaned and saved. The following measurements 

 were taken from these bones (compare figs. 1-8) : 



(1) From the anteriortip of the premaxilla to a median ventral notch in the 



basi-occipital on the margin of the foramen magnum (occipital to 

 maxilla = 0. M.). 



(2) From the ventral notch in the basi-occipital to the anterior margin of the 



hard palate (palate to occipital = P. O.). 



(3) From the anterior tip of the premaxilla to the posterior margin of the 



palate (palate to maxilla = P. M.). 



(4) From the anterior to the posterior margin of the palate (palate = P.). 



(5) The width of the zygomatic arch just behind the molar teeth (zygoma 



anterior = Za.). 



(6) The width of the zygomatic arch just posterior to the pterygoid plates of 



the sphenoid (zygoma, posterior = Zp.). 



(7) The width at third molar teeth, not including the zygoma (teeth = Te). 



(8) The postorbital width of the brain-case (brain-case = Be). 



(9) Width at the auditory meati (ears = E.). 



(10) Height of skull anterior to molar teeth (nose =N.). 



(11) The length of the nasal bone (nasal bone = Na.). 



(12) The length of the mandible (= M,). 



(13) The height of the mandible (= M 2 ). 



(14) The length of the humerus ( = H.). 



(15) Length of ulna (= U.). 



(16) The length of the femur ( = F.). 



(17) The length of the tibia (= T.). 



