OCR Text |
Show 1883.] APPARATUS OF THE TENUIROSTRES. 67 the serpi-hyoid are to be considered as a shifted origin, or as the of an expanding broadened insertion, I am yet unable to decide. M. stylo-hyoideus arises as a broad flattened-out band from the upper margin of tbe occiput, its origin being situated laterad from the end of the thyro-hyal or great cornu of the same side. The muscle then passes underneath (covered by) the parotic gland, crosses the two ribands of the genio-hyoideus of the same side, being directed obliquely forwards and inwards, and is inserted on the sides of the basihyal, laterally and dorsally from tbe greater cornu. This muscle, having its punctum fixum at the occiput, acts as the chief retractor of tbe tongue. M. genio-hyoideus consists of two parts, both of which arise as narrow flat bands from the border and inner margin of tbe mandibles, being thus the most superficial muscles of all on the ventral side between the mandibles. Tbe two bands pass directly backwards along the inner margin of the under jaw, then pass dorsally over the stylo-hyoid and serpi-hyoid. Tbe median portion attaches itself to the distal three quarters of the cerato-branchial, by surrounding or enveloping this bone, being only loosely fastened to it by connective tissue. The outer part accompanies the cerato-branchial throughout its length on the dorsal surface, and is attached to its tip. Both these portions, constituting the genio-hyoid muscle, are surrounded by a common slippery sheath, which compels them to act exclusively in tbe direction of the bone. The muscle has its punctum fixum at its origin at the mandibles, and consequently by its contraction protrudes the tongue. As the cornua of the tongue, surrounded by the genio-hyoid muscle, might be compared to a rod surrounded by an elastic steel spiral fastened to one end of the rod, it will be understood that tbe force with which and the extent to which the tongue can be propelled depends directly on the length of the cornua. This agrees with observation, e. g. Trochilus and Picus compared with Zosterops. M. cerato-glossus. This muscle arises from the distal two thirds of the outer and upper aspect of the thyrohyal, and is attached to the ventral surface of the basihyal. By its contraction it causes the basi- and thyrohyals to be bent at an angle, and thus directs the tip of the tongue. M. tracheo-hyoideus arises from the latero-ventral aspect of the upper part of the trachea, and is inserted into the dorsal surface of the end of the basihyal bone by tbe help of a long aud slender tendon. This muscle acts as a retractor of the tongue when acting at the time with its fellow on the other side ; but when acting singly it directs the tongue to the right or to the left. PROSTHEMADERA. The muscular apparatus of Prosthemadera exhibits some remarkable differences from the arrangement of tbe muscles described above. The mylo-hyoid muscle is not attached to any part of the tongue, but (at least in m y two specimens) is separated from it by a thick 5* |