24 THE VOYAGE OF H.M.S. CHALLENGER. 



Sixteenth Section. — The head is here (Ph VI. fig. 2) cut through where the basis 

 cranii runs upwards into the hollow of the mid-brain ; the top of the ascending ^vall 

 will be seen in the figure of the next section (fig. 3, lo.cl.). Here we have the bent part 

 of the base, close at the back of the pituitary space. 



The pituitary body here shows a racemose structure, and three quasi-glandular 

 lobules are cut through (figs. 2, 2a, py-). The thick sides of the investing cartilage end 

 above in the thin, sinuous alisphenoids [al.s.) ; below, they form the front boundary of 

 the foramina ovalia, but only the orbito-nasal branch of the fifth nerve (fig. 5^) is seen in 

 this section. 



There is a recess, partly membranous {posterior basi-cranial fontanelle, p)-^-C-f.), 

 below and behind the pituitary raceme ; here the notochord {nc.) is cut through at four 

 places ! 



This is one of the most important and instructive parts of this demonstration, and 

 will be more fully illustrated in other sections (the longitudinally vertical) ; but here we 

 can see how suddenly the notochord turns upwards, following the folding of the mid- 

 brain, and also that it turns down again at its apex, ready to follow the folding brain. 



In the fourteenth and fifteenth sections the " epipterygoid " cartilage was seen 

 severed from the apex of the pedicle of the quadrate. Here this "pier" is cut along 

 its most external f)art through the pedicle (pd.), and body (q.), and part of the hinge 

 with the mandible (mk.) is shown. On each side of the larynx the cerato-hyals and 

 first branchials are seen {lx.,c.liy. Ji.hr.). 



Seventeenth Section. — The sections are now becoming very oblique, although parallel 

 with the others ; the top of the huge post-clinoid wall (PI. VI. fig. 3, p.cl.) is cut 

 through, and lower down, the fore part of the investing mass {iv.). Here the alisphenoid 

 (cd.s.) is lower, is very sinuous, and runs into the post-clinoid wall below. 



Below the broad mid-brain (C 2) the infundibular region of the fore-brain {inf.) is 

 seen shining through the slice of the post-clinoid wall behind it. The basilar artery 

 (fig. 3, b.a.) remains in this section, but the cartilage below it is largely cut away. 



At the lower angles of the post-clinoid wall the foramen ovale is cut through, and also 

 the " Gasserian ganglion " (5) ; the root of both the second and third branches is seen 

 curving outwards towards the temjDoral muscle {t.m.). 



The space between the post-clinoid wall and the investing mass has been made by 

 the cutting away of the antero-inferior part of this ascending basis cranii ; this removed 

 part is figured in the last section (fig. 2). The notochord {nc.) lies on the narrow inner 

 part of the investing mass {iv.) ; in front of this part it lay in an oval membranous 

 tract, the posterior basi-cranicd fontanelle, but the moieties of cartilage close in under 

 the median rod ; externally, they are very thick, and are grooved by the internal 

 carotids {i.e.). The cjuadrate cartilage {q.) is here four-sided, the sides being concave, 

 and the angles rounded ofi"; the mandible {mk) is cut through at its posterior part, and 



