OCR Text |
Show 1881.] ANATOMY OF THE ERINACEIDSE. 393 continued forwards between the rami of the mandible, concealing the greater part of the mylo-hyoid muscles (which are very thin, and do not extend beyond the middle of the intermandibular space), and are inserted laterally (under cover of and united at their insertion with the superficial laminae, but extending anteriorly for a short distance beyond them) into the sides of the jaws. This peculiar development of the digastric has been described as an anomaly in man, but is known as a normal condition in Chiromys madagascariensis and in some other Primates'. The writer has found it well marked in certain species of Chiroptera, as in Epomophorus macrocephalus and E. minor, where, although the united internal lamina? of the muscles extend as far backwards as to cover the hyoid bone, there is no connexion with it. It is especially noticeable in this case that the tendinous intersection is vertical, or nearly so, corresponding to the position of the posterior margin of the united muscles, as the oblique intersection in G. raffiesii corresponds to the more anterior position of the posterior margin of the same muscles in the latter species ; and we may reasonably conclude that the tendinous intersection of the digastric, wherever met with in Mammalia-whether as a true tendon, as in the Primates, or as a mere tendinous inscription, as in many species of Chiroptera and of Insectivora-has primarily originated as the origin of a tendinous posterior raphe, such as we find in Gymnura raffiesii2. The sterno-mastoids and cleido-mastoids are large, and, except at their insertions, separate; the cleido-occipital is united for a considerable distance with the trapezius, and really appears to be part of that muscle inserted into the clavicle. The omo-hyoid is well developed, and has the usual origin and insertion. Levator scapula?, from the transverse process and anterior arch of the atlas, is inserted into the extremity of the outer bifurcation of the acromion, superficial to the insertion of the trapezius, to the surface of which its posterior and upper margin is attached. The trapezius is double. Its occipital and cervical portion is well developed, arising from the inner three fourths of the occipital crest, from the centre line of the neck, and from one or two dorsal spines. Some of the anterior fibres separate about the middle of the neck to form the c/e«efo-occipital (or is the cleido-occipital united at this point with the trapezius 1) ; the remaining fibres are inserted into the spine of the scapula from the acromion to its posterior root. The posterior trapezius arises from the last five or six dorsal vertebrae, and is inserted into the posterior third of the spine of the scapula. The rhomboideus anticus has the same origin as the trapezius, with the addition of three or four dorsal spines; it is folded at its insertion into the posterior margin of the scapula. Rhomboideus posticus is a small flat muscle, which passes from the spines of the fourth, fifth, and sixth dorsal vertebrae to the internal surface of the middle of the posterior margin of the scapula beneath tbe r. major. 1 Owen, Comp. Anat. iii. p. 53. - On this subject see my paper "On the Tendinous Intersection of the Digastric," Proc. Roy. Soc. March 31, 1881. PROC. ZOOL. S O C - 1881, No. XXVI. 26 |