iS)6 Me. *•• a. PAKsoifS on ibm [Jan. 14, 



16. The gracilis is usually a double muscle in the Myoinorpha, 

 single in the Lagomorpha. 



The distinctions above given are possibly more numerous than 

 they would be if the opportunity of dissecting a Pika {Lagomys) 

 had presented itself. 



To merely point out the differences between the various sub- 

 orders does not give a just idea of their muscular characteristics. 

 It is necessary also to lay stress on the chief points in which one 

 resembles another and differs from the rest. 



In the first place the Myomorpha resemble 'the Hystricomorpha 

 and differ from both the other suborders in the following points : — 



1. A slip of the masseter passes through the infraorbital 

 foramen. 



2. The three parts of the temporal are more closely fused. 



3. The rectus abdominis often decussates at its origin. 



4. The gracilis is usually double. 



5. The supracondylar slip of the semimembranosus often comes 

 from the caudal vertebrsB. 



The Myomorpha resemble the Seiuromorpha and differ from the 

 other two suborders in the following points : — 



1. The sciuromorphine type of the digastric. 



2. The presence of the transverse mandibular muscle. 



3. The constant presence of the omo-hyoid. 



4. The acromio-trachelian (levator claviculae) always rising from 

 the atlas. 



5. The absence of the scalenus anticus in the Seiuromorpha and 

 in the Myomorpha except the Bathyergiua3 and Oerbillus. 



6. The absence of the scapulo-clavicularis in both, with the 

 exception of the Bathyerginas. 



7. The presence of the two heads to the biceps cubiti. 



8. The presence of the clavo-cucullaris part of the trapezius. 



9. The absence of the splenius colli. 



10. The presence of ischial and caudal heads to the biceps 

 femoris, the latter being often more or less blended with the 

 gluteus maximus. 



11. The fact that the flexor tibialis (flexor longus digitorum) 

 does not join the flexor fibularis (flexor longus hallucis), except in 

 Jthizomys, heteromys, and partly in Pteromys. 



I have been unable to find any point of importance in which 

 the Myomorpha resemble the Lagomorpha and differ from the 

 other two suborders. 



The Hystricomorpha resemble the Lagomorpha and differ from 

 the other two suborders in the following points : — 



1. The presence of the scapulo-clavicularis. 



2. The omo-hyoid is often absent in the Hystricomprpha, always 

 in the Lagomorpha. 



