KEPORT ON THE GREEN TURTLE. 25 



the cerato-hyals and first branchial {chy. Ji.hr.) are also seen in section, the two latter 

 embracing the larynx {Ix). 



Eighteenth Section. — Here (PL VI. fig. 4) only part of the mid-brain (C 2) is 

 figured, and the hind-brain (C 3) without its- cerebellar outgrowths ; the hind half, the 

 Gasserian ganglion, and the root of second and third branches (5), are shown in situ, 

 with the root of this huge segmental nerve on each side springing high up from the 

 substance of the hind-brain (C 3). This is the fore part of the interauditory region, but 

 from the obliquity of the section behind the flexure, the top of the post-clinoid wall, and 

 the fast lessening alisphenoid {p.cl.,al.s.), are still seen. 



The periotic region is cut through, and the anterior semicircular canal (a.s.c.) laid open, 

 crosswise ; here the ganglion geniculatum (8) is cut through in its fore part, and some of 

 the fibres of the " portio mollis " are seen passing into the ear-capsule through the 

 meatus internus. 



The investing mass (w.) is thick at this part, and the notochord [nc.) is partly 

 imbedded in it above. The pedicle of the quadrate (q) is cut off" in front and out- 

 side ; this cartilage is being scooped. In this scooped space the first cleft {cl. 1) is 

 seen, and near the investing mass its inner opening or Eustachian passage is also laid 

 open. 



Nineteenth Section. — Thi» slice (PI. VI. fig. 5) is close in front of the columella. The 

 arch of the anterior semicircular canal, and the ampulla and past of the tube of the 

 horizontal canal {a.s.c, h.s.c), are laid open on each side. 



The space between the capsule and investing mass {iv.) is occupied by the beginning 

 of the seventh and eighth nerves (not shown in this figure), and the facial nerve (7) is 

 laid bare for some extent. It passes under the fore part of the capsule, and appears 

 between the quadrate and the cerato-hyal {q.,c.hy.). Here the quadrate is greatly scooped 

 on its outer face to form the tympanic cavity (c.ty.). 



Twentieth Section. — This is the most imjjortant of the sections of the hind-skull (PI. 

 VI. figs. 6, 6a), for it lays the columella (co.) bare throughout its entire extent, and 

 shows much of the distribution of the "portio mollis" nerve (8). The cavity of the 

 hind-brain (C 3) is laid open, and the roots of the auditory and facial nerves are shown 

 arising from its sides. 



The auditory capsule is here at its widest part, where the "canals" open into the 

 vestibule ; and here the capsule shows three openings, namely, the meatus internus 

 (8), the fenestra ovalis (f.o.), and the fenestra rotunda (f-r.). 



The facial nerve (7) was on the last slice (fig. 5, 7), but the auditory branch (8) is 

 well shown here ; first its broad origin in the medulla oblongata by several roots, next the 

 ganglion geniculatum {g.gc), and then, associated with this by a short string of fibres, the 

 ganglion cochleare {g.cl.), which lies in a pouch-like hollow on the inner face of the capsule. 

 Below this second ganglion the small budding cochlea {cl.) is seen opening infero- 



(ZOOL. CHALL. EXP. PART V. 1880.) E 4 



