OCR Text |
Show 1896.] ANATOMY OE THE HOATZIN. 623 Geniohyoid.-This muscle is in two distinct portions. The posterior division arises from the outer side of the ramus of the iaw, behind the anterior mylohyoid; it passes dorsally to both divisions of the posterior mylohyoid, and, running inwards and backwards, wraps round the ceratohyal to the tip. The anterior portion arises from the inner side of the ramus of the jaw, its edge being superficial to the mylohyoid anterior; it then runs forwards and inwards alongside the posterior division of this muscle, and is inserted to the ceratohyal, partly under and partly distally to the insertion of the posterior division. Gadow ('Das Thierreich,' p. 313) states that the geniohyoid is double in Nectarinia, Otis, Parrots, and Rhea; single in Corvus, Anser, Procellaria, and Spheniscus. Beddard and I found it single in Palamedea; I myself have found it single in Chauna, Rhytidoceros, Cygnus, Pelecanus, and Lophophorus ; double in Struthio, Bromceus, Bhea, Rhynchotus, and Ciconia. It appears as if this muscle were comparable with the latissimus dorsi; originally a diffused sheet it tends to break up into two discrete bands, but there are not sufficient data to draw any inferences of taxonomic value from its double condition in Opisthocomus. The researches of Garrod showed that, in the case of certain notable thigh-muscles, completeness of muscle formulae was, on the whole, primitive, while incompleteness was secondary. In the attempt to extend this view to other muscles it is necessary to remember that many muscles are in process of splitting, and that in these cases increase in number is a sign, not of primitive, but of derivative character. Genioglossus.-At the most this is represented by a few fibres. Ceratoglossus.-This is a very strong muscle, arising from the outer side of the ceratohyal, anterior to the geniohyoids; it passes forwards, superficially to the anterior division of the mylohyoid posterior, and deeply as regards the mylohyoid anterior; ending in a round tendon, it is inserted along the side of the tongue almost to the tip. There is no trace of the division into two, which occurs in Fowls. Ceratohyoid.-This is a strong wide muscle running from the inner side of the ceratohyal, opposite the insertion of the foregoing muscle to the urohyal. The hypoglossals and the system of the sterno-hyoid were present, but the individual muscles were not segmented from each other. Bepressor mandibulae.-A single very large muscle, of which the internal portion is more tendinous, runs from the lateral posterior and under surface of the occiput to the posterior and ventral part of the lower jaw. In Ducks and Geese this muscle is represented by three distinct portions, all of which Beddard and I found in Palamedea \ and described as biventer and digastric. In the Fowls there are at least two portions separable ; in Opisthocomus the tendinous inner portion no doubt represents an inner portion, 1 " On the Anatomy of Palamedea cornuta," P. Z. S. 1894, p. 536. |