384 PROFESSOR OWEN ON THE GENUS DINORNIS. 
the ethmoturbinals of conyolute bony lamine covered with highly vascular pituitary 
membrane. The smaller and more remote anterior turbinal (ib. ao), rarely ossified, 
receives its nerves from the nasal branch (a) of the trigeminal. 
The optic nerve is but one-fifth of a line in diameter, and about half an inch in length 
(Pl. XLV. fig. 4, ¢): its course to the eyeball is shown by dividing and reflecting the 
* obliquus superior” (Pl. XLVI. fig. 2, 0), the “‘rectus superior” (ib. 7), and the naso- 
maxillary division of the trigeminal nerve (ib. w). 
The fifth or trigeminal nerve (Pl. XLV. fig. 1, tr) arises from the ganglionic enlarge- 
ment of the macromyelon in connexion with or covered by the fibres of the transverse 
crus of the cerebellum. After a course of a line and a half, in which it leaves the 
cranium, it divides into two. The upper division (Pl. XLV. fig. 1, w) passes forward, 
ascending obliquely, traverses the orbit, diving beneath the * rectus superior ” (Pl. XLVI. 
fig. 1,7), and the “ obliquus superior” (ib. 0), sending a filament here to the ciliary 
ganglion: it then, emerging at the upper and fore part of the orbit, subdivides. Prior 
to its subdivision it rests internally on the dura mater, closing an unossified part of the 
cranial wall external to the large rhinencephalic fossa. The branch (Pl. XLV. 
figs. 1 & 2,x, and Pl. XLVI. figs. 1 & 2, 2) here reenters, as it were, the cranium, and 
emerges external to the cribriform plate by a canal larger than any of the olfactory 
foramina. The canal perforates the lacrymal bone, then grooves the outside of the tur- 
binal mass (a), and next perforates the base of the maxillary branch of the nasal: after- 
wards, inclining mesiad and sinking into the naso-premaxillary cavity, it gives branches 
to the anterior turbinal (ib. ao), attaching itself to the septum narium, near the lower 
margin, aud becoming lost upon the septal membrane. 
The branch (Pl. XLV. figs. 1 & 2,y) passes more directly forward, impresses the 
outer side of the upper (ae) and middle (az) turbinals, and is continued more super- 
ficially beneath the horny sheath of the beak as far as the terminal disk perforated by 
the nostrils; it is diminished by filaments given off to the formative membrane and 
softer layer of the sheath to its termination at the tactile disk. The division corre- 
sponding to that called ‘“ third division,” or “ inferior maxillary nerve” (fig. 1, 6), sends 
off two nerves to the muscles of the mandible ; these are derived from the non-ganglionic 
origin of the trigeminal: the main part, from the ganglion, is continued forward, 
sending off a branch to the outer tegument at the base of the mandible; it then enters 
the mandibular canal (fig. 1, z), and is continued forward to the end of the mandible. 
The “eighth” nerve arises by two sets of roots from the same macromyelonal tract— 
the anterior set of three (Pl. XLV. fig. 1,1), and the posterior one of two filaments 
(ib.2): these combine in passing out of the skull, and emerge at the ‘“ vagal” foramen, 
whence the nerve (ib.3) is continued further than usual before swelling into the 
ganglion and dividing into the glossopharyngeal (ib.4) and the pneumogastric (ib. 5; 
see also figs. 1 & 2in Pl. XLVI.). I need not go into the further distribution of 
these nerves, as they cease to mark any part of the skeleton. 
