268 PROF. W. K. PARKER ON THE STRUCTURE AND 
evidently a reptile, and nearly half its length is due to the growth of the coiled tail. 
The number of somatomes has greatly increased, and the lobes of the face are now 
confluent; yet the mesocephalic flexure is still perfect, throwing the huge mid brain 
(Pl. LXIL. fig. 3, C’) forwards, as though it were the end of the embryo. ‘The 
hemispheres (C"") are very much elongated in front of the pineal region (pl); the 
hind brain (C’) is still very long and thinly covered. 
The prenasal beak is now definitely formed, and projects considerably beyond the 
brain, so that the outer nostrils (ol,¢.) are carried away from the eyeballs; these 
latter are immense, and are fitted with well-margined sockets. 
The auditory capsules (aw) are still evident as ovoidal swellings on the outside, and 
the involution (aqg.v) is evident as a lipped slit; a curtain hangs down over the closed 
first cleft. 
The mouth (figs. 3, 4, m) is now well formed and has large angles; the mandibles 
(mn) are still short as compared with the upper or maxillo-palatine margin of the 
mouth; the hyoid (Ay) lies some distance behind the mandibles, and the clefts are 
nearly closed. When the inferior arches are removed, and the head is viewed from 
below (Pl. LXIII. fig. 3), we see how much the palatine region has developed in front 
of the pituitary involution’ (py). 
At the mid line, where the faucial and palatine territories meet, there is a sagitti- 
form recess, in the centre of which the pituitary rudiment is to be found. 
The hinder tract is short, and passes right and left into the clefts, the first of which 
(cl') only is figured; it lies within and behind the mandible (mn). The epiblastic 
mucous membrane in front of this pair of clefts is now greatly elongated, narrows 
towards the front, and then widens again somewhat. In each angle, in front, the 
lacrymal “involutions” (/.7) are seen. Right and left, the club-shaped maxillo-palatine 
folds (mx.p) are growing inwards, especially in front, and these inner lobes contain 
the rudiments of the hard palate. The upper palatine skin shows a median seam when 
the two sides have grown together. ‘The nasal sacs and their openings (0/, e.m) are still 
quite inferior in position, and the lobes of the fronto-nasal process (f.n.p) are growing 
small; they now form the anterior margin of the palate, where the promaxillary teeth 
will be. 
When the palatal and faucial skin has been removed, then the hardening basis 
cranii is exposed (Pl. LXIII. fig. 4); in relation to the early chondrocranium of the 
Vertebrata, genérally, this is a very important dissection. 
At present the notochord (ne) is half as long as the whole basal tract; it was two 
‘ In my earlier papers I have been in the habit of calling certain passages about and in front of the mouth, as 
well as the mouth itself, by the term “clefts.” Now, and for the future, I shall only call those passages clefts 
that lie behind the mouth, and in which the epiblast unites with the hypoblast. In the mouth, pituitary 
rudiment, lachrymal, and nasal passages, the whole tract, outside and in, is merely epiblast; these will be 
called “ involutions.” 
