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Show 1866.] ON THE ANATOMY OF THE CRESTED AGOUTI. 393 P.c). It corresponds very nearly to our description of the same muscle in Hyrax*. It is also wonderfully strong in the Rodents selected for comparison, most so perhaps in the Guinea-pig. The latissimus dorsi takes origin from the dorsal and lumbar vertebrae, and is likewise attached by a fascia to the surface of the infraspinatus muscle. It has an insertion by tendon, as usual, in common with the teres major (figs. 2 & 3, L. d.). It sends off a small dorso-epitrochlear slip (figs. 2 & 3, D.e.) to the ulnar side of the olecranon. This last we noticed in the Guinea-pig, but not clearly in the specimens of Rabbit and Hare. The trapezius is very extensive and elongated (fig. 3, Tra.). Muscular fibres come from the spines of the fourth to the eleventh dorsal vertebrae, covering the latissimus dorsi, and proceeding outwards and forwards are partially inserted into about the middle of the spine of the scapula. A strong tendinous fascia continues onwards, joining the almost distinct anterior portion, which may be said to arise from the occiput and ligamentum nuchae, to be inserted into the anterior edge of the spine of the scapula and metacromion process, a slip of fibres proceeding down the side of the limb as far as the middle of the humerus. In the neck the fibres join those of the levator claviculse. There is no characteristic difference in the Guinea-pig. In the Hare the nuchal portion is very thin, and the dorsal portion goes as far backwards as the twelfth or thirteenth vertebra. In the Rabbit this muscle appears to join the latissimus dorsi posteriorly. In neither of these three animals is the long humeral slip so strongly developed as in the Agouti. Rhomboideus. There is no distinction between the rhomboideus major, minor, and capitis ; but one continuous sheet of muscle arises from the paramastoid process of the occiput, the median line of the neck, and the dorsal vertebrae. Its insertion is into the vertebral border of the scapula. Meckel says (loc. cit. p. 242), "Le Pore-epic et la Marmote parmi les Rongeurs n'ont qu'un rhomboide, mais il y est tres-developpe, il vient de 1'arcade de l'occipital," &c. In the Hare, Rabbit, and Guinea-pig we find a distinct rhomboideus capitis muscle, which arises by delicate narrow fibres from the occiput, and, broadening as it proceeds backwards and outwards, is inserted into the anterior end of the vertebral border of the scapula. In them also the rhomboideus major and minor are interblended. The serratus magnus and the levator anguli scapular, indivisibly united together, form another extensive layer of muscle. Origin : the transverse processes of all the cervical vertebrae and the first eight ribs. Insertion : the spinal border of the scapula beneath the rhomboideus. In the Guinea-pig, Rabbit, and Hare there is a line of separation between the serratus magnus and levator anguli scapulas, opposite the third rib ; the last portion has the greatest amount of attachment to the scapula. * P. Z. S. 1865, p. 335. PROC. ZOOL. Soc-1866, No. XXVI. |