OCR Text |
Show 1880.] VARIATION IN EQUUS ASINUS. 5 masses of laminae of epithelial debris. The dilatatores naris vary their arrangement in relation to this pouch ; thus, ordinarily a continuous series of fibres extends to it from above, behind, and below, being the superior and inferior dilators. But we have seen excessive development of the band against the cul-de-sac of the pouch and deficiency of the other parts of the series. The posterior extremity of retractor labii superioris has sometimes a muscular addendum connecting it with the zygomatic ridge. Mylohyoideus varies somewhat in being divided generally at its anterior part into two distinct planes. Geniohyoideus sometimes sends a small distinct band to genioglossus at about the centre of the intermaxillary space. Hyopharyngeus, in addition to its usual attachment to the inferior part of internal surface of superior third of stylohyal, has often another one, quite distinct from the inferior third. W e more frequently see the latter in the Horse. Hyoideus parvus sometimes absent. Hyoglossus brevis sometimes attached to stylohyoid, generally not. Arytcenopharyngeus is occasionally well marked. Retractor oculi may form a complete investment of the optic nerve, or consist of four bands corresponding with the recti. The middle oblique muscle of the eye, as described by Strangeways, occasionally occurs in the Ass. The inferior opening of the lachrymal ductus ad nasum varies in position ; generally it opens at the upper part of the anterior naris, thus differing remarkably from the same structure in the Horse. Neck.-Levator humeri never shows the fibrous band indicative of the seat of the clavicle, which this muscle has in the Ox, Pig, and other Ungulates ; but this information is conveyed in some subjects, in which we have seen a small muscle running from levator humeri around the anterior part of pectoralis anticus to the inner side of that muscle, where it disappears. Serratus magnus has sometimes a distinct rudimentary division passing to second cervical transverse process, generally only extends as far forwards as the third (see arrangement in Ox). Scalenus: instead of terminating by each head at the first rib as in the Horse, the superior division may be prolonged to the third rib or even further back (see arrangement in Ox) over serratus magnus. Longus colli we have seen attached only beneath the five anterior instead of the six anterior dorsal vertebrae. Back.-Transversalis costarum posteriorly in some cases is large and muscular and blended with longissimus dorsi in the lumbar region ; in others it is tendinous and inserted into first lumbar transverse process. Serratus posticus minor varies considerably in its development and attachments. Latissimus dorsi just before its insertion into the humerus varies in its relations with scapulo-ulnaris. Sometimes serial muscular |