OCR Text |
Show 1884.] MR. G. E. DOBSON ON CAPROMYS MELANURUS. 239 clavicle as far as the origin of the cleido-mastoid, under cover levator claviculee. The clavicular part of this muscle evidently corresponds to the cleido-occipital which is united with it. Trapezius posticus has a very extensive origin, arising as far forwards as the posterior origin of the tr. anticus (with which it may almost be said to be continuous), and extending to the commencement of the lumbar aponeurosis, quite covering the anterior half of the latissimus dorsi. Bhomboideus anticus and rh. posticus are represented by a single muscle arising from the inner third of the occipital crest and from the centre line of the neck, to the first and second dorsal spines. The anterior half of the muscle is very thin, the posterior much thicker ; all the fibres are inserted into the internal and posterointernal border of the scapula. Serratus magnus is overlapped by the posterior margin of the levator angula scapula. It arises from the cartilages of the first to the sixth ribs and is inserted as usual. Levator angula scapula arises from the transverse processes of the third to the seventh cervical vertebras, and is closely connected throughout its origin with the scalenus medius. Scalenus anticus absent, as shown by the position of the brachial plexus. Sc. medius (fig. 1, sc.m) and sc.posticus appear to be united ; they are inserted into the cartilages of the fourth to the sixth ribs. Muscles of the Fore Limb. Pectoralis major (fig. 1, p-p") arises in four parts-three sternal from the whole length of the sternum and aponeurosis of the external oblique, and one clavicular. Of the sternal the anterior (p) arises from the anterior extremity of the manubrium sterni and as far back as the middle of the sternum under cover of the origin of the sterno-facialis, and, uniting with the clavicular part, is inserted with it into the middle of the shaft of the humerus along with the deltoid ; the middle part arises behind the preceding as a strap-shaped muscle (p"), which is inserted under cover of it into the shaft of the humerus and into the internal tuberosity ; and the posterior (p"f), broader, from the last bone of the sternum and from the aponeurosis of the external oblique muscle, is inserted under cover of the middle part into the internal tuberosity higher up. The clavicular part arises from the outer third of the clavicle, becomes connected with the anterior division of the sternal part below, and, above, with the lower margin of the deltoid, and is inserted as above described. Pectoralis minor (fig. 1, piv)- This is represented by a completely separate strap-shaped muscle arising from the cartilages of the third to the sixth ribs, and inserted into the outer third of the clavicle and acromion under cover of the origin of the clavicular part of the pectoralis major. This is precisely as we find it in Dasyprocta cristata. Deltoid arises from the acromion process (being connected by its |