| OCR Text |
Show 1894.] MYOLOGY OF RODENTS. 295 15. The supracondylar slip of the semimembranosus is either separate or connected to the rest of the muscle in the Hystricomorpha. 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 Hystricomorpha. Dipodidae.-The Dipodidae, as has been pointed out, agree with the Hystricomorpha in the arrangement of the masseter and in tbe 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-clavicularis. They present in addition the following characteristics:-(1) The teres 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 ulna. (3) The supinator longus is present. (4) The trapezius is in two portions. (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. (10) There is no peroneus quiuti digiti. (11) The omo-hyoid is present. Octodonticlce.-(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 haUucis 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 differences between the muscles of the Ground- and Tree-Porcupines. Whether these differences 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:-(1) The digastric differs in Hystrix and Sphingurus. (2) The omo-hyoid is rudimentary in Hystrix, large in the Tree-Porcupines. (3) The levator claviculae 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* |
