188 ME. F, G. PABSONS ON THB [Jan. 14, 



7. The claviculo-s'capularis is absent in the My oinorpha, present 

 in the Hystrieomorpha. 



8. lu the Myomorpha the three parts of the deltoid lie close 

 together. In the Hystrieomorpha they are separated by distinct 

 intervals. 



9. The biceps ciibiti has two heads in the Myomorpha. In the 

 Hystrieomorpha there may be one or two. 



10. The Myomorpha seldom have the first part of the coraco- 

 brachialis, in the Hystrieomorpha it is often present. 



11. The spleDius colli is never found in the Myomorpha, in the 

 Hystrieomorpha it is sometimes seen. 



12. The two parts of the biceps femoris are usually distinct 

 in the Hystrieomorpha. In ' the Myomorpha they are seldom 

 separable. 



13. In the Myomorpha the flexor tibialis and flexor fibularia 

 do not usually join in the sole. In the Hystrieomorpha they are 

 always united. 



14. In the Myomorpha the accessorius is absent or very ill- 

 developed. In the Hystrieomorpha it is present and well 

 marked. 



Differences between the M yomorpha and the Sciuromorpha. 



1. The three parts of the temporal muscle are more closely 

 fused in the Myomorpha than in the Sciuromorpha. 



2. A small part of the masseter passes through the infraorbital 

 foramen in the Myomorpha. No part passes through in the 

 Sciuromorpha. 



3. The three parts of the deltoid are more closely fused in the 

 Myomorpha than in the Sciuromorpha. 



4. In the Myomorpha a rotator humeri is only found in the 

 Cricetina3. In the Sciuromorpha it is always present. 



5. In the Myomorpha the flexor sublimis digitorum sends no 

 slip to the fifth digit. In the Sciuromorpha this slip is present. 



6. The supinator longus is absent in the Myomorpha, but is 

 present in the Sciuromorpha except Castor^. 



7. The extensor longus digitorum always sends a tendon to the 

 fifth digit in the Sciuromorpha ; this tendon is often absent in the 

 Myomorpha. 



8. The rectus abdominis often decussates at its origin with its 

 fellow in the Myomorpha. There is no decussation in the Sciuro- 

 morpha. 



9. The quadratus femoris is triangular in the Myomorpha, 

 quadrilateral in the Sciuromorpha. 



10. The supracondylar slip of the semi-membranosus always 

 i-ises from the tuber ischii and is closely connected to the 

 adductors in the Sciuromoi-pha. In the Myomorpha it may rise 

 from the tuber or caudal vei-tebrse and is distinct from the 

 adductor mass. 



' Macalister describes an exceedingly feeble supinator longus in the Beaver 

 (' Morphology of Vertebrate Animals,' p. 289). 



