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Show 256 MR. P. G. PARSONS ON T H E [Mar. 20, 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 stylohyoid, 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 paroccipital 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 tbe Dipodidae the muscles are of equal size ; the sterno-mastoid 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 Hystricidas and Chinchillidae the muscles are normal, except that in the Chinchilla they are inserted into the back of the great tympanic bulla. In the Dasyproctidas the cleido-mastoid is small and rises from the middle of the clavicle near the junction of the bony and ligamentous parts (Dasyprocta, Ccelogenys). 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 tbe 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 innermost 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 tbe 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. |