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Show 1891.] ON THE VARIATION OF THE LEPORINE STERNUM. 159 Fig. 4. Alligator mississippiensis, juv. of 112 centim. total length. Floor of chamber, as seen from above, after the removal of the olfactory mucous membrane and the underlying cartilaginous floor of the olfactory capsule. (A portion of the latter, which was left in position, is indicated at ns.f.) Nat. size. Caiman niger. Comparison dissection to fig. 4 ; dried skull only. One-third nat size. Alligator mississippiensis, juv. Premaxillo-maxillary suture with parts adjacent, ventral aspect. Three times nat. size. Caiman niger. Premaxillo-maxillary suture with adjacent parts, for comparison with fig. 6. Ventral aspect. One-half nat. size. Hyla ccerulea. Mandibular symphysis, with related structures. Anterior aspect. Three times nat. size. Fig. 5. Fig. 6. Fig. 7. Fig. 8. ap. c.s fb. f-P-fpC fpl". Jr. ig-m. b. m.m. mx. na. n. p. n.s n.s' n.s n j Reference Letters. Anterior orifice of Jacobson's organ. Orifice of vomerine sac (? Jacobson's organ). Naso-palatine (Stenson's) canal, cartilaginous wall of. Symphysial fibrous pad. Premaxillary foramen. Prepalatine foramen. Postpalatine foramen. Frontal. Jacobson's cartilage. Vomerine ligament. Basi-mandibular cartilage. Mento-Meckelian bone. Maxilla. Nasal. Postei'ior nares. ns.f. pi. pm. p.p. pt. i.mp. sn. vo'. vo". vo Septum nasi. Alary cartilage. Alary cartilage, internal, lamina of. Floor of cartilaginous olfactory capsule. Palatine. Premaxilla. Palatine process of premaxilla. Pterygoid. Maxillo-palatine suture. Maxillary sinus. Body of vomer. Wing of vomer (osseous floor of postnarial portion of olfactory chamber). Palatine lobe of vomer. 2. On the Variation and Development of the Leporine Sternum. By R. H. BURNE, B.A. Oxonv F.Z.S. [Eeceived February 17, 1891.] The mammalian sternum has been shown by Ruge1 to be entirely costal in origin. The ventral ends of each pair of ribs come into apposition and subsequently fuse in the middle line to form, by ossification and segmentation, a sternebra; each sternebra is a product of the pair of ribs immediately behind it. This holds good for the whole sternum, with the exception of its most anterior segment or manubrium: that, although in M a n a product of the first two pairs of ribs, and therefore serially homologous with a couple of the sternebrse, is still further a compound structure, for Goette2 has shown that it may embody (Talpa) the remnant of the episternum (interclavicle3) of the lower Vertebrata. 1 " Untersuchg. ii. d. Entwickelungsvg. am Brustbein," Morph. Jahrbuch, pp. 373 et seq. (1880). 2 Archiv f. Anat. u. Phys., Bd. xiv. p. 563 (1877). 3 Howes has recently suggested that this may be the vanishing vestige of a caracoidal archisternum of the lchthyopsida (' Nature,' vol. xliii. p. 269, 1891). |