1898.] ANATOMY or PEDETES CATTEB. 873 



not always absent in the Hystricomorpha, but it is always 

 present in the Myomorpha. 

 4. The presence of "a splenius colh. This is not a very 

 important point, but 1 have never yet found the muscle 

 among the Myomorpha. 



The most important Myomorphine characteristics are : — 



1. The arrangement of the depressor mandibulse (digastric). 



This has the tendinous arcade and fused anterior bellies so 

 characteristic of myomorphine and sciuromorphine rodents. 



2. The absence of a scalenus ventrahs. This muscle is not 



always present in the Hystricomorpha, but it is always absent 

 in the Myomorpha. 



3. The absence of a claviculo-scapularis, a muscle which was 



always found in the Hystricomorpha but never in the 

 Myomorpha. 



4. The'flexor tibiahs does not unite with the flexor flbularis in 



the sole as it usually does in the Hystricomorpha. Dobson 

 made a great point of the value of these tendons for 

 classificatory purposes, but I have met with evidence to 

 show that it is not altogether reliable. 



5. The biceps cubiti (flexor longus cubiti) has two heads : this 



arrangement is almost invariable among the Myomorpha, 

 but it also sometimes occurs in the Hystricomorpha. 



With regard to the relationship of Pedetes with the Dipodidte, 

 the following resemblances are important and suggestive : — 



1. There is a tendinous arcade in the digastric and the anterior 



bellies are in contact. 



2. There is no claviculo-scapularis. 



3. The origin of the omo-trachehan (levator claviculse) is from 



the atlas. 



4. The rectus ventralis does not decussate with its fellow in 



front of the pubic arch. 



The following, on the other hand, are points in which Pedetes 

 differs from the Dipodidae : — 



1. The scalenus ventralis (anticus) does not rise from the basi- 



occipital bone. 



2. There are two heads to the biceps cubiti (flexor longus 



cubiti). 



3. There is no transversus mandibulse. 



4. There is no omo-hyoid. 



5. The splenius colli is present. 



• 6. The flexor tibialis does not join the flexor fibularis in the 

 sole. 



I am of opinion that a careful comparison of the muscles 

 of Pedetes with those of other Eodents shows that it is allied 

 Peoc. Zool. Soc— 1898, No. LVIII. 58 



