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Show 1903.] THE MUSCLES OF THE UNGULATA. 289 Rectus ventrcdis {R. abdominis).-This, as usual, rises from the ventral aspect of the pubis near the symphysis and is continued forward to the first rib. Ventral to the anterior two or three ribs it lies deep to the supracostalis, and here its fleshy fibres usually cease and it is continued to the first rib by a thin aponeurosis. Many authors describe it as ending at the third, fourth, or fifth ribs, but wherever we have been able to repeat their dissections we have always been able to make out a delicate continuation of the muscle to the first rib. The number of linea? transversa? varies from five to ten but eight or nine is the commonest number; they are, however, not well marked, and Steel (XIX.) has pointed out that in the Ass their number varies in individual specimens. Pyramidalis.-We have never seen this muscle in Ungulates, and our experience agrees with that of Lesbres (V.) and Meckel (VII.). Mivart and Murie (XXIV.) were certain of its presence in Hyrax, but in our specimen it was undoubtedly absent. All the preceding ventro-lateral muscles of the belly-wall are supplied by the intercostal nerves. Quadratus lumborum.-This is a much narrower muscle in the Ungulata than in Man, and is attached posteriorly, by a narrow tendon, to the sacro-iliac joint or to a tubercle on the ilium close by. Anteriorly it is inserted into the lumbar transverse processes, and usually into the heads of several of the last ribs. In the Hyrax (74) it goes to the posterior twelve ribs, in the Chevrotain (20) into five, in the Horse (64, 65), Pig (4), and Elephant (81) into two, while in the Bovida? its costal insertion seldom extends beyond the last rib. Psoas magnus.-This rises from the transverse processes of all the lumbar vertebra? as well as from the sides of the bodies, it often also rises from a few of the lower thoracic bodies; its insertion is as usual into the lesser trochanter. In the Hippopotamus (1) it comes from the last two thoracic as well as the lumbar vertebra?. In the Pig (9, 11) it is not well developed and only comes from the lumbar region. In the Elephant (81) its attachment seems to be the most extensive, as in that animal it rises as far forward as the last four thoracic vertebra? as well as the last four ribs near their heads. The Psoas parvus was present in every animal of which we have records except the Red River-Hog (11), and we have no doubt of its being a very constant muscle in Ungulates ; it rises from the bodies of the last three or four thoracic, and several of the lumbar vertebra?; it is inserted by a ribbon-like tendon into the ilio-pectineal eminence. The Iliacus is a small muscle and is laterally compressed; it rises from the iliac fossa, the ventral sacro-iliac ligament, and the margin of the sacrum. Before its insertion it blends with the psoas. Murie, in the Giraffe ( X X X I L ) , noticed that the iliac and sacral origins remained separate for some time, and we found the same in the Harnessed Antelope (55), though it certainly is not always the case in Ungulates. P R O C . ZOOL. Soc-1903, V O L . II. No. XIX. 19 |
