1891.] ON THE VARIATION OF THE LEPORINE SIEKNUM. 159 



Fig. 4. Alligator mississippiensis, Juv. of \\'2centim. total length. Floor of olfac- 

 tory chamber, as seen from above, after the removal of the olfactory 

 mucous membrane and the underlying cartil.iginous floor of the 

 olfactory capsule. (A portion of the latter, whiL'li was left in position, 

 is indicated at ns.f.) Nat. si~e. 



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

 fhird nat size. 



Fig. 6. Alligator mississippieiisis, jiip. 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. Hyta cmrulea. Mandibular symphyses, with related structures. 

 Anterior aspect. Three times nat. size. 



Ee/erence Letters. 



a.f. An terior orifice of Jacobson's | n.s'. Septum nasi. 



organ. | n.s". Alary cartilage. 



ap. Orifice of vomerine sac n.s'". Alary cartilage, internal, 



(? Jacobson's organ). 

 c.s. Naso-palatine (Stenson's) 

 canal, cartilaginous wall 

 of. 

 fh. Symphysial fibrous pad. 

 f.p. Premaxillary foramen. 

 f.pl'. Prepalatine foramen. 

 f.pl". Postpalatine foramen. 

 fr. Frontal. 

 jo. Jacobson's cartilage. 

 Ig. Vomerine ligament. 

 m.h. Basi -mandibular cartilage. 

 m.m. Mento-Meekelian bone. 

 7nx. Maxilla. 

 na. Nasal. 

 n. p. Posterior nares. 



lamiia of. 

 ns.f. Floor of cartilaginous 

 olfactory capsule. 

 2)1. Palatine. 

 pm. Preniaxilla. 



p.p. Palatine process of pre- 

 maxilla. 

 pt. Pterygoid. 

 s.7np. Maxillo-palatine suture. 

 sn. Maxillary sinus. 

 vo' . Body of vomer. 

 vo" . Wing of vomer (osseous 

 floor of postnarial portion 

 of olfactory chamber). 

 vo"' . Palatine lobe of vomer. 



2. On the Variation and Development of the Leporine 

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



[Eeceived February 17, 1891.] 



The mammalian sternum has been shown by Ruge^ to be entirely 

 costal in origin. The ventral ends of each pair of libs come into 

 apposition and subsequently fuse iu the mi Idle 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 sternehrse, is still further a compound 

 structure, for Goette" has shown that it may embody (Talpa) the 

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



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

 pp. 37o 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 arehisternum of the Ichthyopsida (' Nature,' vol. xhii. p. 269, 1891). 



