1901.] 



NATURAL SCIENCES OP PHILADELPIIfA. 



46? 



ni.c. — Cartilage of lower jaw 

 n.c. — Na«al cartilage. 

 0. — CEsophagus. 

 I. — Olfactory lobes. 

 'p.n. — Posterior nares. 

 r.n.a. — Kight nasal aperture. 

 r.n.c. — Right nasal canal. 

 r.ii.g. — Eight nasal gland. 

 s. — Nasal septum. 



s.c. — Spinal cord. 



t. — Tongue. 



ta. — Trachea. 



t.r. — Tooth rudiment. 



v.c. — Vertebral column. 



v.p. — Ventral passage. 



X. — Septum projecting back between 



main nasal canal and its side 



branch. 



EXPLANATION OF PLATE XXIV. 



(All sections icere drawn with a Zeiss Camera.) 



Fig. \a. — Side view, from a photograph, of an embryo of the stage repre- 

 gented in the sections. The yolk is not represented, but the cut stalk may 

 be seen projecting from the abdominal wall just anterior to the hind legs 

 (mag. f diam.). 



Fig. 16. — This is merely an outline drawing of the preceding figure to 

 show the planes of the sections represented in the following figures. 



Fig. 2a. — Transver.>e section through the tip of the snout. The section is 

 so near the tip of the snout, that it does not cut the lower jaw (mag. 4 

 diam.). 



Fig. 2h. — Transverse section posterior to fig. \a. It passes through the 

 extreme tip of the lower jaw (mag. 4 diam.). 



Fig. 2c. — Transverse section still further toward the base of the snout. 

 The details of the figure will be understood from the lettering (mag. 4 

 diam.). 



Fig. 2d. — Transverse section posterior to the preceding (mag. 4 diam.). 



Figs. 21 to h. — Transverse sections posterior to the preceding, passing 

 through the right eye, but anterior to the left eye (mag. 4 diam.). 



Fig. 2J. — Transverse section passing through the .extreme posterior part of 

 the main nasal passages (l.n.c. and r.n.c). The section passes through the 

 anterior edge of the left eye and through the anterior ends of the olfactory 

 lobes (mag. 4 diam.). 



Fig. 2/. — Transverse section just beyond the posterior end of the main 

 nasal cavities. It passes through the extreme posterior ends of the lateral 

 nasal cartilages {n.c.) (mag. 4 diam.). 



Fig. 2k. — Transverse section through the point where the two ventral 

 canals (yp.) unite to form a single large median canal. The section 

 passes through the eyes at about their central points, and shows the sets of 

 muscles by which their motion is controlled. The lower jaw is cut at the 

 point at which it becomes continuovis with the neck, which accounts for the 

 break in the ventral side of this and the following figure (mag. 4 diam.). 



Fig. 21. — Transverse section, a short distance posterior to the one immedi- 

 ately preceding, passing through the posterior nares (p.n.), and through 

 the upper end of the trachea {ta.) which appears in the figure to be three 

 distinct cavities (mag. 4 diam.). 



Fig. "ia. — Horizontal section through the plane a-&, fig. \h. Shows the 

 general anatomy of the head as seen in horizontal section, and especially the 

 way in which the main nasal passages {l.n.c. and r.n.c.) curve outward 

 and forward, as has been above described (mag. 4 diam.). 



Fig. 4a. — Transverse section, under a much greater magnification, to 

 show the structure and position of the paired Jacobsou's organ (j.) (mag. 

 18 diam.). 



