REPORT ON THE GREEN TURTLE. 33 



passing forwards, and escaping under the narrow bridge of cartilage ; these two nerves 

 are the sixth or " abducentes," and are on their way to the " external rectus " muscle of 

 the eyeball ; they come from the base of the medulla olalongata between the roots, of the 

 fifth and seventh, and are probably the " anterior roots " of one or both of these nerves 

 (Milnes Marshall). 



Ninth Section. — Here (PL IX. fig. 3, 3«) the nasal passages are seen passing into the 

 posterior or internal nares (i.n.), between which the palatal covering of the septum nasi 

 is seen. Between the lowest part of the nasal cavities a 'passage is seen — the "middle 

 nasal passage" [m.n.p.) ; it is half-way between the prenasal cartilage {2^-n.) and the 

 openings of the nasal passages behind. This is also seen in the palatal view of the skull 

 (PI. IV. fig. 7). 



Behind the nasal outlets the palate is open ; this is the pituitary space (^^y.), and at 

 a shorter distance behind this space the notochord is seen invested with its own and its 

 mesoblastic sheath. Right and left, we see the beginning of the pterygoid bone (^xy.), 

 and outside it is the epipterygoid cartilage {e.pg.) now seen to be continuous with the 

 pedicle of the quadrate {^pd.,q.), which is cut through along its greatest length above the 

 tympanic excavation ; between the pedicle and the auditory capsule we see the Eustachian 

 passages (cl. 1). 



In this section, as in the last, we see the cartilaginous sheath of the notochord (iic, 

 s.nc.) quite distinct from the paired cartilages that correspond to the neural arches of the 

 spine ; it is, however, thin, and the cells of it are flat. 



Tenth Section. — The lining skin of the floor of the mouth appears in this slice (PI. 

 IX. fig. 4), and the upper lip, lower jaw, tongue, and larynx ((mx.p.,mn.,tg.,lx.) are here 

 indicated in relation. The bulging middle third of the investing mass is here seen, with 

 the corresponding part of the notochord {iv.,nc.) ; and behind, the medulla oblongata is 

 passing into the myelon {my.) through the foramen magnum. The part of the investing 

 mass here sho'WTi has coalesced with the auditory capsule close inside the rudiment of the 

 cochlea {cl.) ; opposite this sac the end of the columella (co.) is seen cut across, and the 

 lower part of the posterior canal (j).s.c.) is laid bare. The thick sides of the occipital 

 arch (e.o.) are shown coalescing with the auditory capsule (an.), and outside the latter 

 the quadrate (q.) is displayed in its most hollow part. 



Eleventh Section. — A little below the last, parts are seen in the next figure (fig. 5) 

 that help greatly to a true understanding of the skull at this stage. Much of the mouth 

 {m.) is shown, with its bordering tissues {mx.p.), but the mandible now is seen com- 

 pletely running up to the thick lower part of the quadrate {q.). 



Behind the quadrate all but the proximal end of the columella [co.) is seen ; its top 

 was shown in the last section (fig. 4, co.) ; the lower part of the first cleft {cl. 1) is seen 

 between the quadrate and the columella ; and in the space behind it, and between the 

 floor of the ear-capsule and the occipital arch, the ninth, tenth, and twelfth nerves aie 



(ZOOL. CHAI.L. EXP. — PAKT V. 1880.) E 5 



