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Show 1866.] ON THE ANATOMY OF THE CRESTED AGOUTI. 391 from the inside of the sternum, opposite the cartilage of the first rib, and, continuing forwards (upwards) closely united in part, ultimately separate and have their usual insertions. The same in the Hare and Guinea-pig. The omo-hyoid is wanting. The levator clavicular is very remarkable in having an origin by tendon from the basis cranii, immediately to the inner side of the auditory bullae and directly behind the tendon of the anomalous scalenus anticus. It is inserted into the clavicle, towards its outer end, immediately opposite the origin of the fourth part of the pectoralis major. O n the right side we found this muscle closely adherent to the cleido-mastoid above; but near the clavicle the external jugular vein and carotid artery separated them, after which the two muscles proceeded side by side to the somewhat rudimentary clavicle, the levator claviculse being inserted outermost. O n the left side we found no such union with the cleido-mastoid above; but instead the muscle divided (at the anterior third of the distance between the atlas and clavicle), its broader portion, partly adherent to the trapezius, passing over the shoulder-joint onwards as far as the proximal end of the forearm, simulating a cephalo-humeral (figs. 2 & 3, L. c). But we believe it cannot be a cephalo-humeral, because there is a distinct cleido-mastoid, as before described, entirely distinct and superficial to this abnormally enlarged portion of the levator claviculee. It is this portion which evidently has led Meckel* to consider this muscle to be represented by the anterior part of the trapezius in the Agouti. Prof. Owen*)* makes mention of the levator claviculae being present in two specimens of the Dasyprocta acuschy (111.) dissected by him. W e ourselves noted its existence in the Guinea-pig, Hare, and Rabbit,-in the former being inserted into the metacromion process of the scapula; in the two latter it is carried, along with the trapezius, over the shoulder-joint, fibres passing to the upper part of the humerus. In the Hare the levator claviculae is like that which we found on the left side of Dasyprocta cristata, but without the long descending portion to the forearm, rather stopping short at the metacromion process. The rectus capitis anticus major is but indistinctly separated from the longus colli, unless what we have called the scalenus anticus should in reality be this muscle, the insertion % of which, however, it must be remembered, is into the first rib, therefore entirely different from that of the rectus capitis anticus major as it ordinarily exists in man. Should our interpretation be correct, the muscle in ques- * Op. cit. vol. vi. p. 239. t P. Z. S. 1830-31, p. 76. X' Speaking generally, the insertion is oftener to be relied on as indicative of homology than the origin of a muscle-although, perhaps, this rule is more strictly applicable to the limbs than elsewhere. |
