GROWTH AND MORPHOLOGICAL CHARACTERS. 65 



The measurements considered in the tables are as follows : 



Skull measurements: 



1. Median sagittal length, from cranial edge of fused premaxillary 



bones to lambdoidal ridge of occipital bone. 



2. From the same cranial edge to the ventrocranial edge of the 



foramen magnum. 



3. Length of the zygomatic arch from the laterocaudal margin of 



the infraorbital foramen to the caudal margin of the mandibular 

 fossa. 



4. From the laterocaudal margin of the infraorbital foramen to 



the exoccipital bone immediately dorsad of the jugular process. 



5. Fropi the premaxillary bone to the medial lachrymal sulcus. 



6. From the premaxillary bone to the medial caudal margin of 



the palatine bone. 



7. From the caudal edge of the foramen incisivum to the ventro- 



cranial edge of the foramen magnum. 



8. Width immediately craniad of the external acoustic pore. 



9. Width at caudal portion of zygomatic arch, where skull is 



broadest. 



10. Width at cranial edge or point of the zygomatic bone. 



11. Width at laterocaudal margin of infraorbital foramen. 

 Mandibular measurements: 



12. Extreme length from angular process to laterocaudal margin 



of incisor alveolus. 



13. From concave edge between condyloid process and angular 



process to cranial edge of first molar alveolus. 

 Humerus: 



14. Length, from fossa between greater and lesser tuberosity to 



fossa between capitulum and trochlea. 

 Femur: 



15. Length, from trochanteric fossa to intercondyloid fossa. 

 Tibia: 



16. Length, from fossa between spine of tibia and lateral tuberosity 



to lateral concavity at distal end. 



COMPARISON OF SKELETAL DIMENSIONS. 

 The Avebagb Dimensions. 

 The wild C. rufescens has long been known and recorded by taxono- 

 mists as a small cavy species, smaller than the guinea-pig, C. porcellus. 

 Hence, the average skeletal dimensions given in tables 63 and 64 were 

 not taken from individual, small specimens that may have been wide 

 variates. Other wild skeletons were examined and measured, but were 

 omitted for the sake of accuracy in these averages because a few sutures 

 were not closed, although they were sexually mature. They were in 

 reality smaller than the average recorded. A number of fully adult 

 living specimens were carefully examined both in our own laboratory 

 and in European collections and were clearly much smaller than the 

 guinea-pig. The wild, which enter intd the averages in tables 63 and 

 64, were the two original wild parents used to propagate the wild stock 

 in captivity, and all of their sons (cr24 and cf 33) who, with their 



