456 
MR. W. K. PARKER OK THE DEVELOPMENT 
Section 7. Here (Plate 31, fig. 7) those bands ( p.pg.) are free, and the trabeculae (tr.) 
look like two flat, partly confluent bricks, gently bent round the base of the mem- 
brano-cranium. The section of the palatine bars, now very slender, is circular. 
Section 8. In this section (Plate 31, fig. 8) the eye (e.) is cut through its middle, 
and the mandible, very short as yet, has come into view ; here, of course, the mouth 
cavity (m.) is shown. The pineal body ( pnl .) and the fore part of the mid brain can 
just be seen, as well as the back part of the hemisphere (C la .), running into the thala- 
mencephalon below. The trabeculae (tr.) do not now follow the convexity of the 
membrano-cranium, but are flat and horizontally placed ; they are distinct here, and 
oval in section. The palatine bars (ppg.) are now round in section, and are more than 
twice their own diameter from the trabeculae. Below the mouth cavity (m.) the man¬ 
dibles (mk. ) are cut through obliquely ; they are rounded rods, similar to the palatines 
at the same part. 
Section 9. The ninth section (Plate 31, tig. 9) is through the mid brain (C 2 .) and 
the thalamencephalon (C 1 .). The trabeculae (tr.) are now nearly cylindrical, and are a 
distance apart equal to twice their own thickness. Between them a thin lamina of bone 
is cut through ; this is the parasphenoid (pa.s.). Outside the oral cavity (m.) the 
palato-quadrate cartilages (p-pgk) are seen to be flattened and concavo-convex, the 
convex side being turned inwards. On each side, below the mouth, the mandibles (mk.) 
are cut through obliquely. Above, in the superorbital region, the rudiment of the 
tegmen cranii is seen as a narrow band of cartilage—flat outside and convex within. 
Section 10.'—In the next section (Plate 31, fig. 10) the swelling mid brain (C 2 .) 
reaches the superorbital bands on each side; the trabeculae (tr.) are nearly twice as far 
apart as in the last, and are quite circular in section. Between and below them the 
parasphenoid (pa.s.) is twice as wide as in the last. This section shows the articular 
end of the mandible (ar.c.) joined to the hinge on the quadrate end (q.) of the palato- 
quadrate pier ; this part is now high, flattened, and convexo-concave, with the con¬ 
cavity on the outside. 
Section 11. — This is through the widest part of the mid brain (Plate 31, fig. 11, 
C 2 .), the thalamencephalon (C 1 .), the infundibulum (inf.), and the distinct pituitary 
body (py.). The superorbital bands are flatter and nearly vertical in position ; the 
trabeculae (tr.) are now furthest from the mid line; the parasphenoid bone is still 
visible below the pituitary body ; and the convexo-concave quadrates (q.) are now cut 
through behind the mandible at the mid line below the mouth (m.). The tongue (tg.) 
is cut through in front of its cartilaginous core. 
Section 12.—The next slice is through the hind brain (Plate 31, fig. 12, C 3 .), the 
front part of the auditory capsule (vb.), and the fore end of the notochord ( nc .). On 
each side of the hind brain there is a large mass of nerve-cells, the rudiment of the 
ganglia of the trigeminal and facial nerves (Y., YII.). 
The investing mass (iv.), wide up to its fore end, and not embracing the ascending 
apex of the notochord (nc.), is a rather thick plate of cartilage; the inner edge of each 
