OCR Text |
Show 1902.] JACOBSON IN THE ELEPHANT-SHREW. 225 Parker has shown that in the allied genera Petrodromus and Rhynchocyon there are a considerable number of Marsupial characters. In the Hedgehog the organ is formed on the common Eutherian type, and I expected to find in Macroscelides indications of marsupial affinity. W h e n the organ was investigated, however, it was seen to be quite different from that in any Eutherian hitherto examined, and to be typically Marsupial in almost every respect. Before entering upon comparative observations, it will be convenient first to describe the condition of parts in Macroscelides. If a section be made near the middle of the proboscis, it will be seen (PL X X I . fig. 2) to be formed of a ring of cartilage (a.n.), enclosing the two nasal passages and surrounded by soft tissues- muscles, tendons, and skin. The skeletal portion is made up of a well-developed median nasal septum (n.s.) and two alinasals (a.n.), which sweep round from the upper end of the septum and meet each other inferiorly. From this lower point of union of the alinasals they pass upwards to meet the lower end of the septum. From the inner side of each alinasal, near the level of the base of the septum, there passes inwards a small turbinal which is an anterior continuation of the inferior nasal turbinal; and from the point where the incurved end of each alinasal meets the base of the septum there passes downwards and outwards a second turbinal plate which may be referred to as the septal turbinal (s.t.). With very little modification, this description might refer to any section of the proboscis. On approaching the anterior end (PL X X I . fig. 1), however, the turbinals are found to be less developed, the nasal septum slender and fused with the alinasals inferiorly, and the upper half of the alinasals to be separated from the lower. Near the anterior na al opening a transverse section shows a pair of alinasals above, a pair of cartilages on the nasal floor, and a pair of rather complicated lateral cartilages which apparently form nasal valves. The anterior nasal opening looks outwards and slightly downwards. In a transverse section near the root of the proboscis, the only noteworthy differences from the more anterior sections are that the base of the septum is considerably larger, while the lower halves of the alinasals are not only separate from each other, but are distinct from the alinasals above-forming nasal-floor cartilages. W h e n the plane of the premaxilla is reached (PL X X I . fig. 3), the outer and lower part of the nasal-floor cartilage becomes lost, only the part situated immediately below the base of the septum and which forms the septal turbinal remaining. A few sections in front of the plane where the palatine process is given off from the premaxilla, the premaxilla (pmx.) sends upwards a narrow plate as a support to the inner side of each of the two cartilages which lie at the base of the septum. These plates form the anterior ends of the palatine processes (p.p.). About this same plane the small cartilaginous plates, which in the |