OCR Text |
Show 392 MR. G. E. DOBSON ON THE [Mar. 1, the zygoma and the margin of the orbit. All four muscles form very long and slender tendons, which pass forward horizontally parallel to one another, to be inserted respectively into the upper lip, slightly in front of the first upper incisor, into the extremity of the nose below the nasal orifice, into the middle of the alae nasi, and into the extremity of the nose above the nasal orifice. Between the origins of the zygomaticus major and minor arises another muscle, the levator labii superioris et erector vibrissarum, which passes directly forwards between the tendons of these muscles, and terminates in a mass of muscular fibres which invest the bases of the remarkably long vibrissae which spring from the sides of the muzzle, and is also connected with the orbicularis oris beneath. The levator labii superioris proprius is well developed, arising from the maxillary bone above, and in front of the infraorbital foramen, forming a strong tendon, which, united over the extremity of the muzzle with the tendon of the corresponding muscle of the opposite side (as in Equus), is inserted with it into the upper lip below the nasal orifices. The temporal muscle is remarkable for its great size and peculiar development. It arises by three heads, which are all inserted into the coronoid process :- I. From the greatly developed occipital crest and surface of the parietal bones, in the usual position of origin, inserted into the superior and anterior margin of the coronoid process. II. From the mastoid process, root and upper margin of the zygoma along its posterior two thirds, the fibres curve upwards, forwards, and downwards, forming a semicircular muscular mass above the zygoma on the side of the head, lying against the temporal muscle proper; inserted into the outer side of the coronoid process near its base. III. From the inner side of the posterior two thirds of the zygomatic arch a mass of muscular fibres arises, which, curving forwards, is inserted into the postero-external margin of the upper half of the coronoid process. W e have thus a series of muscular structures having an exceedingly extended origin, and of great relative development, attached to the much-expanded coronoid process of the mandible, supplying the force needed to move such greatly extended jaws; for, probably, in no other mammal are these so much developed in comparison with the size of the animal. Not less remarkable in its development is the digastric. This muscle 'arises normally; but at the point where the tendinous intersection occurs (nearly opposite the hyoid bone) it splits into two laminae: one, superficial and external, continues forward in the usual direction of the muscle ; the other, transverse, is directed inwards, and slightly forwards, its posterior free tendinous margin being a direct continuation of the tendinous intersection of the muscle, which unites in the middle line in front of the hyoid bone with that of the corresponding muscle of the opposite side, forming a tendinous raphe, from which the united muscles are |