OCR Text |
Show 338 MR. A. H. GARROD ON THE [Apr. 4, In Plotus this uniformity is considerably disturbed, irrespective of the above-described kink, by the excessive development of the longus colli in its lower almost interthoracic portion, as well as, though to a less degree, by the enlargement of the longus colli posterior behind. In Plotus anhinga, as above stated, there are 20 cervical vertebrae. A small slip of the longus colli arises from the body of the third dorsal vertebra, which is inserted into the transverse process of the 17th cervical. Above, and in contact with this, is another similar slip to the 16th cervical. From the bodies of the 2nd and 1st dorsal vertebrae, as well as from the antero-median portions of the six lower cervical vertebrae, a large muscle arises on each side, in layers (somewhat resembling the layers formed by the basally expanded petioles of an onion bulb)-the lower being partially enclosed in the upper-which ultimately form a bipenniform mass with a tendon running axially through it and continually receiving additions in the form of outer coverings of tendinous tissue arising from the enclosing muscles, till it forms a strong single tendon which courses up the front of the neck, close to the middle line on each side, to be inserted into the downward-directed, peculiarly long haemapophysial spine of the 8th cervical vertebra, and gives off slips, on its way up, to the serially homologous processes of the 9th and 10th vertebrae. A similar tendinous slip to the lith vertebra has an independent origin from the bodies of the 15th and 16th vertebrae, internal to the main muscular mass, which is almost the size of a lemon, and with its fellow of the opposite side, of much the same shape, filling up and projecting beyond the slight anterior concavity above mentioned, formed by the mutual articulations of the 15th, 16th, 17th, 18th, and 19th cervical vertebrae. (In Plate X X V I . figs. 1 & 2, these different details are clearly shown.) Posterior cervical region.-Here there is an exaggerated development of muscle in the juxta-thoracic part, opposite the similar enlargement in front, although it is not so considerable behind. The longus colli posterior is the muscle which is excessively developed. It becomes differentiated from the posterior dorso-spinal mass opposite the 14th and 15th cervical vertebrae to run up the neck in the form of a fleshy belly which receives additional origins, in the form of muscular slips, from the vertebrae as high as the 9th cervical. Where the slip from the 10th vertebra (which is a small one) joins it, the muscle becomes tendinous, forming a rounded cord, to the inner side of which the large fasciculus from the 9th vertebra is attached. A reference to the account given above of the disposition of the vertebrae in this region will make it evident that the tendon of the longus colli posterior must make a considerable backward turn opposite the transverse line of articulation between the 8th and 9th cervicals-because there the two bones meet at a considerable angle, with the genu directed forwards. This being the case, some special mechanism is essential to prevent the tendon from breaking away from the vertebral column when the muscle with which it is |