1896.] MioLOsr of rodents. 187 



The union of the tendons in the sole has been already alluded 

 to as not being entirely confined to the Hystricomorpha. 



In the following points the Dipodidee resemble the Myo- 

 morpha : — 



1. The sciuromorphine arrangement of the digastric. 



2. The presence of a transverse mandibular muscle. 



3. The absence of the scapulo-clavicularis. 



4. The presence of the omo-hyoid. 



5. The absence of the splenius colli. 



6. The origin of the levator claviculoe (acromio-trachelian) from 

 the atlas. 



The first three of these are very important and constant 

 points, the latter three are sometimes noted in the Hystrico- 

 morpha. 



On the whole I think that the myological points in favour of 

 myomorphine tendencies for the Dipodidas are far stronger than 

 those in favour of hystricoraorphine. 



Genbeai. Summaet of Muscles of Eodbnts. 



In order to complete my paper I propose to give a series of 

 lists of the different points in which the four suborders of Eodents 

 differ from and resemble one another, though the following pages 

 are only tentative, and liable to require rearrangement as further 

 material is added. They may, however, piove useful in directing 

 the attention of future observers to the muscles deserving of 

 special notice from a classificatory point of view, and they may 

 also be of service in showing the nnisclea that are constant in 

 Eodents nearly related, whatever their mode of life may be, aud 

 that may turn out to be equally constant in nearly related groups 

 belonging to other orders. 



In a former contribution' the differences between the Hystrico- 

 morpha and Sciuromorpha are summarized. 



Differences between the Myomorplia and Ilystncomorpha. 



1. The part of the masseter which passes through the infra- 

 orbital foramen is usually small in the Myomorpha, large in the 

 Hystricomorpha. 



2. The Myomorpha have the sciuromorphine arrangement of the 

 digastric. 



3. The transverse mandibular muscle is present in the Myo- 

 morpha, absent in the Hystricomorpha. 



4. The omo-hyoid muscle is always present in the Myomorpha, 

 and may be present or absent in the Hystricomorpha. 



5. The acromio-traihelian (levator claviculse) always rises from 

 the arch of the atlas in Ihe Myomorpha. In the Hystricomorpha 

 it sometimes rises from the basioccipital. 



6. The scalenus anticus is usually absent in the Myomorpha, 

 usually present in the Hystricomorpha. 



> P.Z.S. 1894,p.294. 



