OCR Text |
Show 1881.] ANATOMY OF THE ERINACEIDsE. 405 the shortness of the xiphisternum ; and the mesosternum is made up of three or two segments only. The pelvic opening contrasts remarkably with that of Gymnura; its transverse diameter, measured between the acetabula, is nearly or quite half its longitudinal, whereas in G. raffiesii it is scarcely one ninth ; the symphysis pubis is also much deeper, especially in E. europceus; the tuber ischii is short and rounded off; and the posterior margin of the ramus of the pubis and ischium is convex, not concave. Except in E. europa?us and its varieties, there is a supracondylar foramen in the humerus. The carpus is formed on the same plan as in Gymnura; but the scaphoid and lunar bones are early united, leaving no trace of their original separate condition. In the femur the convexity which in Gymnura represents a third trochanter is less prominent and more extended, indicating a long muscular, as opposed to a tendinous, insertion of the muscles attached to it, and pointing to the less active habits of the animals. Other limb bones, both in the anterior and posterior legs, are generally similar to those of Gymnura, a single departure from the typical number of five digits in the fore and hind feet being seen in E. heterodactylus and its varieties, where the hallux is altogether wanting. In the muscular anatomy the chief differences between the species of this genus and Gymnura are found in the much greater development of the panniculus carnosus, and in other minor points to be noticed further on. To the cutaneous muscles described in Gymnura raffiesii there are in all the species of Erinaceus others superadded, which are related to the well-known defensive attitude assumed by these animals when frightened. They have been figured in the anatomical plates of Cuvier and Laurillard \ and described by Prof. Huxley 2. In the general myology the following differences are especially noticeable:- In the face the zygomaticus major is inserted into the orbicularis oris and integument of the upper lip at a short distance in front of the angle of the mouth. The temporal muscle arises also from the zygomatic arch, as in Gymnura ; but its fibres do not take origin so far back as the mastoid process. The digastric is single, and does not unite with its fellow of the opposite side between the jaws; it has nearly the same calibre throughout, but is crossed about the middle by an oblique tendinous inscription, corresponding precisely iu position to the tendinous intersection in Gymnura. The mylohyoid is well developed, consisting of an anterior and posterior portion. Cleido-occipital is slender and quite unconnected with the trapezius. The serratus magnus is not united with the levator anguli scapula?. The pyramidales are well developed, in striking contrast with Gymnura, in which they are rudimentary or absent. The recti abdominis et stemalis are connected with the pubic bones by three instead of four tendons, the missiug tendon corresponding to the 1 Planches dc Myologie. 3 Anat. Vert. Animals, p. 445. |