1894.] MYOLOGY OF BOBEKTS. 25? 



In Pteromys the sternohyoid is inserted by a thin tendon. 



Omo-hyoid. — The omo-hyoid may be present or not. When 

 it is present it has the human attachments to the hyoid bone and 

 anterior border of the scapula, but it never has any tendinous 

 interval ; it runs, moreover, a straight course between its two 

 attachments. 



In the Dipodidae it is present (B. cegyptius, D. hirtipes, Alectaga 

 indica ; in the last it is specially well marked). 



In the Octodontidse it is not constant. In Octodon and Ca- 

 promys it is feebly developed, in Myopotamus it is absent, while in 

 Aulacodus it is well marked. In the Hystrieidae it is well marked 

 in Sphingurus aud Erethizon 1 , but in Hystrix it was seen as a thin 

 layer of muscular fibres disappearing in the fascia under the sterno- 

 mastoid. 



In the Chinchillidae and Dasyproctidae it is absent (Chinchilla, 

 Lagostomus, Dasyprocta, Ccelogenys). 



In the Caviidae it is also absent (Cavia cobaya, Ceredon rupestris, 

 Dolichotis). 



In the Sciuromorpha it is always present (Sciurus, Pteromys, 

 Xerus, Spermophilus, Aretomys, Castor). 



Levator Claviculce. — The levator claviculae rises either from the 

 basioccipital behind the origin of the scalenus anticus, or from the 

 ventral arch of the atlas ; it is inserted chiefly into the acromion 

 and rnet acromion and the fascia of the shoulder, but sometimes it 

 extends to the acromial end of the clavicle. It is supplied by 

 branches from the cervical plexus. 



In the Dipodidae it rises from the front of the atlas and runs 

 to the outer end of the clavicle. In the Octodontidse it is not 

 constant. In Aulacodus, Capromys melanurus 2 , and Myopotamus 

 it rises from the basioccipital, but in Octodon from the atlas. In 

 the Hystrieidae it rises from the atlas in Sphingurus and Erethizon 3 , 

 but in Hystrix it comes from the base of the skull and is inserted 

 into the acromion and fascia of the arm as low as the elbow. (See 

 fig. 10.) 



In the Chinchillidae it rises from the atlas in Chinchilla, and 

 from the basioccipital in the Viscacha; in the latter animal it 

 is inserted into the outer half of the clavicle as well as the 

 metacromion. 



In the Dasyproctidae it rose from the atlas in the specimen of 

 D. cristata which I dissected ; in the specimen dissected by Mivart 

 and Murie it rose from the basioccipital 4 . In Ccelogenys it rises 

 from the basioccipital and is very large. 



In the Caviidae it rises from the basioccipital in C. cobaya, 

 Ceredon rupestris, and Dolichotis. 



In all the Sciuromorpha it rises from the atlas and is inserted 

 into the metacromion, never seeming to reach the clavicle. In 



1 Journal of Anatomy, vol. xxii. p. 126. 



2 Dobson, P. Z. S. 1884, p. 234. 



3 Mivart, P. Z. S. 1882, p. 271. 



4 P. Z. S. 1866, p. 383. 



