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Show 1896.] ANATOMY OF PETROGALE XANTHOPUS. 693 THE MUSCULAR SYSTEM. Muscles of the Head and Neck. The Temporal has the usual attachments ; it rises as far back as the occipital curved line and as far forwards as the level of the postorbital process of the zygoma ; the two muscles of opposite sides do not meet in the middle line of the head. The Masseter is divisible into anterior and posterior portions ; the former, which corresponds to the anterior superficial part of Eodents, rises by tendon from the projecting zygomatic process of the maxilla and is chiefly inserted into the inflected angle of the mandible ; it is not very satisfactorily separated from the posterior part, which shows signs of being divided into a postero-superficial and a postero-deep portion by a layer of tendon. The Internal Pterygoid is very large while the external is quite small. The Sterno-mastoid runs from the front of the presternum to the paramastoid process. The Cleido-mastoid rises from the middle of the clavicle and is inserted just behind the last, with which it is unconnected ; it is pierced by the spinal accessory nerve. The Sterno-hyoid and Thyroid are normal; the latter has a tendinous intersection about its middle. The Omo-hyoid is a flat ribbon-like muscle which has the usual attachments to the scapular and hyoid bone; it, as well as the last two muscles, are supplied by branches from the 1st and 2nd cervical nerves direct, instead of through the medium of the hypoglossal. There is no central tendon. The Bigastrlc rises from the tip of the paroccipital process and is inserted into the mandible midway between the angle and the symphysis. There is no distinct tendon, but a small fibrous patch exists above and below, about the middle. It has the usual double nerve-supply. The Stylo-glossus is the only styloid muscle which is well marked ; it rises from a tubercle on the anterior border of the paroccipital process. The Mylo-hyoid extends almost as far forward as the symphysis. There is no Transverse mandibular muscle. The Hyo-glossus rises from the hyoid bone and from the raphe in front of it; it lies deep to the genio-hyoid, but superficial to the genio-hyo-glossus. The Acromio-trachelian rises from the 1st, 2nd, 3rd, and 4th cervical transverse processes, and is inserted into the acromion and outer third of the spine of the scapula ; it is entirely covered by the trapezius, into which some of its superficial fibres are inserted. Macalister1 says that it rises from the first three cervical vertebrae in Bennett's Wallaby, and from the first two in the Great Kaugaroo. ' Ann. & Mag. Nat. Hist. ser. 4, v. p. 154 (1870). |
