1894.] MYOLOGY OF RODENTS. 295 



15. The supracondylar slip of the semimembrauosus is either 

 separate or connected to the rest of the muscle in the Hystrico- 

 morpha. In the Sciuromorpha it is fused with the adductors, but 

 has a distinct nerve supply. 



16. The flexor longus digitorum joins the flexor longus hallucis 

 in the sole in the Hystricomorpha. In the Sciuromorpha the two 

 muscles do not join. 



B. Chief characteristics of the different Families of the 

 Hystricomorijha. 



Dipodidce. — The Dipodidte, as has been pointed out, agree with 

 the Hystricomorpha in the an-angement of the masseter and in 

 the tendons of the foot, but differ from them and approach the 

 Sciuromorpha in the arrangement of the digastric, in the presence 

 of a transverse mandibular muscle, and in the absence of the 

 scapulo-cluvicularis. They present in addition the following 

 characteristics : — (1) The tei-es major is inserted posteriorly to the 

 latissimus dorsi. (2; There is only the long head to the biceps 

 cubiti, which is inserted chiefly into the ulua. (3) The supinator 

 longus is present. (4) The trapezius is in two poi-tions. (5) There 

 is no bony insertion to the gluteus maximus. (6) The scansorius 

 is distinct. (7) The supracondylar slip of the semimembranosus 

 rises from the tuber ischii. (8) The extensor proprius hallucis is 

 absent. (9) The peroneus brevis is absent. (iO) There is no 

 peroneus quinti digiti. (11) The omo-hyoid is present. 



Octodontidce. — (1) The teres major is inserted in front of the 

 latissimus dorsi. (2) Both heads of the biceps cubiti are present, 

 and the muscle is inserted into the radius and ulua. (3) The 

 coraco-brachialis only consists of the second part. (4) The flexor 

 sublimis digitorum gives no slip to the fifth finger. (5) The flexor 

 profundus digitorum sends a slip to the thumb. (6) The trapezius 

 is undivided. (7) The rectus abdominis decussates at its origin with 

 the opposite muscle. (8) The gluteus medius does not rise from 

 the ilium. (9) The scansorius is not a distinct muscle. (10) The 

 extensor proprius hallucis communicates with the extensor longus 

 digitorum on the dorsum of the second toe. 



Hystricidce. — It is difficult to point out many points which are 

 characteristic of the Porcupines as a group, owing to the great dif- 

 ferences between the muscles of the Ground- and Tree-Porcupines. 

 Whether these diffei-ences are due to their different mode of life, 

 or indicate that the animals are less nearly allied than the genera 

 of other families, requires further investigation to determine. The 

 following are some of the chief distinctions :—(l) The digastric 

 differs in Hystrix and S^Mngurus. (2) The omo-hyoid is rudi- 

 mentary in Hystrix, large in the Tree-Porcupines. (3) The levator 

 davicute comes from the skull in Hystrix, from the atlas in the 

 Tree-Porcupines. (4) The two parts of the sterno-scapularis 

 are continuous in Hystrix, separate in Sphingurus. (5) The 

 biceps cubiti has one head in Hystrix, two in the Tree-Porcupines. 

 ^ 20* 



