1891.] ON THE VARIATION OF THE LEPORINE STERNUM. 



159 



Fig. 4. Alligator iTiississippiensis, juv. of 112 centim. totallength. Floor of olfac- 

 tory 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 ws./.) Nat. size. 



Fig. 5. Caiman niger. Comparison dissection to fig. 4 ; dried skull only. One- 

 third nat size. 



Fig. 6. Alligator mississippiensis, jiiv. Premaxillo-maxillary suture with parts 

 adjacent, ventral aspect. Three times nat. size. 



Fig. 7. Caiman niger. Premaxillo-maxillary suture with adjacent parts, for 

 comparison with fig. 6. Ventral aspect. One-half nat. size. 



Fig. 8. Hyla ccerulea. Mandibular symphysis, with related structures. 

 Anterior aspect. Three times nat. size. 



Eeference Letters. 



.«.;■ 



•ap. 



Anterior orifice of Jacobson's 



organ. 

 Orifice of vomerine sac 

 (? Jacobson's organ). 

 ■c.s^ Naso-palatine (Stenson's) 

 canal, cartilaginous wall 

 of. 

 fb. Symphysial fibrous pad. 

 f.p. Premaxillary foramen. 

 f.pl'. Prepalatine foramen. 

 f.pl". Postpalatine foramen. 

 fr. Frontal. 

 jc. Jacobson's cartilage. 

 Ig. Vomerine ligament. 

 m.h. Basi-mandibular cartilage. 

 in.7n. Mento-Meckelian bone. 

 mx. Maxilla. 

 na. Nasal. 

 «. p. Posterior nares. 



n.s'. Septum nasi. 

 n.s". Alary cartilage. 

 n.s"\ Alary cartilage, internal, 

 lamina of. 

 as.f. Floor of cartilaginous 

 olfactory capsule. 

 pi. Palatine. 

 pm. Premaxilla. 



p.p. Palatine process of pre- 

 maxiUa. 

 pt. Pterygoid. 

 s.mp. Maxillo -palatine suture. 

 sn. Maxillary sinus. 

 vo' . Body of vomer. 

 vo". Wing of vomer (osseous 

 floor of postnarial portion 

 of olfactory chamber), 

 tio'". Palatine lobe of vomer. 



2. On the Variation and Development of the Leporine 

 Sternum. By E. H. Burne, B.A. Oxon., F.Z.S. 



[Eeceived February 17, 1891.] 



The mamTnalian sternum has been shown by Ruge^ 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 Man a 

 product of the first two pairs of ribs, and therefore serially homo- 

 logous with a couple of the sternebrse, is still further a compound 

 structure, for Goette^ has shown that it may embody {Taipei) the 

 remnant of the episternum (interclavicle^) of the lower Vertebrata. 



1 " Untersuchg. u. d. Entwickelungsvg. am Brustbein," Morph. Jahrbuch, 

 pp. 373 et seq. (1880), 

 ■ * Archiv f. Anat. u. Phys., Bd. xiv. p. 563 (1877). 



^ Howes has recently suggested that this may be the vanishing vestige of a 

 coracoidal archisternum of the Ichthyopsida (' Nature,' vol. xliii. p. 269, 1891). 



