REPOET ON THE GREEN TURTLE. 11 



The first azygous part to be noticed is tlie upper or the pineal gland {^jnl.) ; it runs up 

 ])etween the mid-brain and the hemispheres (C 2, C la) ; the second is below, and will 

 be the infundibulum (inf.). The hindmost pair of vesicles are largely constricted off as 

 the essential part of the eyeball ; their constricted stem is the hollow optic nerve (2) ; 

 this tube is close in front of the beginning of the infundibulum. 



In front, as the external views also show, the fore-bi'ain has budded into the hemi- 

 spheres, right and left (C la) ; behind, where the solid olfactory nerves are given ofl', 

 a rudimentary olfactory vesicle (C lb) has appeared ; it is, however, now, and for a 

 long time to come, quite distinct from the nerve itself (1), whose fil^res grow downwards 

 and backwards. 



The chondrocranium, of necessity, is greatly modified by the folded form of the 

 neural vesicles that are suj)ported by it ; it follows, very accurately on the whole, the 

 elegant curves of the lower surface of the brain. 



The notochord (iic) lies above and between the moieties of the investing mass (iv.), 

 but where these parts are at their greatest height in the mesocephalic hollow space, 

 the notochord retreats, and then curves forwards, like a semi-erect caterpillar ; its end 

 is bulbous. 



In front of this ascending part the skull floor is open (figs. 2-4), for here the oral 

 involution is intussuscepted, and here the internal carotid arteries {i.e.) enter. 



Cartilage, however, is seen at the mid-line in this section (fig. 4, i.tr.) ; this will 

 be understood better by reference to the bird's-eye view (fig. 5). 



In front, the section is a little on the near side of the middle, so that the prenasal 

 cartilage (figs. 5-7, p.n.) is not seen, but the solid olfactory nerve, and the beginning 

 of the rhinencephalon, or olfactory bulb, are brought into view. 



The cavity of the mouth is seen to be bounded in front by the retral fronto-nasal 

 process [n.f.]).), on its sides by the maxillo-palatine fold (mx.p.), and behind by the 

 inferior arches, two of which, the mandible [mn.) and the hyoid (%.), are shown in 

 section in the floor of the throat. 



When this small head is scalped, and the brain removed, then the post-pituitary 

 wall (ji.cl.) is the highest part of the object, and two retreating floors are seen, the 

 one in front and the other behind (fig. 5). 



This high thick wall is cartilaginous in its middle part, and is strongly buttressed 

 by tissue growing in on each side between the eye and the ear (e.,au.). 



Only the hinder part of the notochord is seen, the fore part is towards the observer ; 

 its investing cartilages (iv.) are seen in the occipital and hind part of the basisphenoidal 

 regions as a pair of broad plates. 



Each of these plates is crescentically cut away in two places ; the hinder or larger 

 emargination is in relation to the egg-shaped ear-ball (au.) ; and the first notch which 

 goes further in, is for the exit of the large trigeminal nerve (5). 



