256 me. p. g. paesons on thb [Mar. 20, x 



laginous rod joining the hyoid bone to the skull and is inserted 

 into the tongue. 



The stylo-pharyngeus has pratically the same origin as the stylo- 

 hyoid, but is seldom well marked. The animal in which it was 

 most clearly seen was Sphingurus. 



Sterno- and Cleido-mastoid. — These two muscles are distinct 

 in their whole length. Except in the exact origin of the cleido- 

 mastoid they are subject to very little variation. 



The sterno-mastoid rises from the side of the anterior portion 

 of the sternum, and is inserted into the side of the paroceipital 

 process and the curved line of the occipital bone running inwards 

 from this. The cleido-mastoid rises from the bony clavicle and is 

 inserted nearer the middle line (dorsal) and often under cover of 

 the sterno-mastoid. In all cases the spinal accessory nerve runs 

 deep to both muscles and supplies them entirely. 



In the Dipodidae the muscles are of equal size ; the sterno-mas- 

 toid is inserted ventral to the cleido-mastoid and does not cover it. 

 The cleido-mastoid rises from the middle third of the clavicle in 

 D. cegyptius and D. hirtipes, but from the outer third in Alectaga 

 indica. 



In the Octodontidae the cleido-mastoid rises from the inner third 

 of the clavicle and at its insertion overlaps the sterno-mastoid 

 instead of being overlapped. In the Hystricidae and Chinchillidae 

 the muscles are normal, except that in the Chinchilla they are 

 inserted into the back of the great tympanic bulla. 



In the Dasyproctidae the cleido-mastoid is small and rises from 

 the middle of the clavicle near the junction of the bony and liga- 

 mentous parts (Dasyprocta, Coelogenys). 



In the Caviidae the two muscles are separated by a much greater 

 interval than in other cases. The cleido-mastoid is the larger and 

 runs from the rudimentary clavicle to the curved line of the 

 occipital bone internal to the insertion of the sterno-mastoid. The 

 two muscles are separated by a larger interval in Ceredon rupestris 

 than in Cavia cobaya ; in the latter the origin of the cleido-mastoid 

 blends with the deltoid. 



In the Sciuromorpha the two muscles are much more fused 

 towards their insertion, the cleido-mastoid rising from the inner- 

 most part of the clavicle. 



In Arctomys, Xerus, and Spermophilus there seem to be two 

 cleido-mastoids, owing to some of the fibres of the trapezius being 

 separated from the rest by the levator claviculae (see Trapezius). 

 In Castor the sterno-mastoid has a large origin from the ventral 

 surface of the presternum overlapping the pectoralis. The cleido- 

 mastoid rises from the inner half of the clavicle. 



Sterno-hyoid and Thyroid. — These muscles present the human 

 attachments and characteristics. 



In Myopotamus the sterno-hyoid is inserted into the hyoid bone 

 and raphe between the mylo-hyoids for some distance, so that the 

 borders near the insertion become superior and inferior instead of 

 lateral. In the Caviidae the sterno-thyroid is very small. 



