REPORT ON THE GREEN TURTLE, 49 



Fifth Stage. 1^ inch long. — The carapace and limbs are now well formed, but the 

 abdominal region is still membranous. The large head is rapidly approaching the adult 

 form, but the mid-brain still projects. The mandibles now fill in the triangular space 

 between the maxillo-palatines, which have converged to form the upper jaw ; above their 

 junction is a median nasal passage. The chondrocranium is well formed, but is at present 

 only an open trough, except in the superoccipital region ; the orbito- and alisphenoids 

 are continuous with each other, with the post-clinoid w^all, and with the auditory capsules. 

 The notochord is only half as high as the post-clinoid wall, and curves over, having an 

 elongated cartilaginous sheath, which passes down beyond it, behind the pituitary body ; 

 the latter is closely applied to the infundibulum, but not united with it. The orbito-nasal 

 septum is now developed. There is no ossification in the chondrocranium, but osteo- 

 blasts are quite evident in the pterygoids, and the other investing bones appear as 

 granular tracts. The epipterygoid is continuous with the pedicle of the quadrate. 

 Meckel's cartilages are confluent, and the columella is in two segments, as in the 

 Batrachia (Pis. III.-IX.). 



Sixth Stage. 3 inches long, head 7 lines long. — The general form of the head is like 

 that of the adult ; ossification has commenced in the exoccipitals, basioccipital, and basi- 

 sphenoid, and the investing bones are all present. There is no distinction between the 

 nasal and prefrontal, and the parietal has grown down between the second and fifth 

 nerves, so as to abort nearly the whole of the alisphenoid ; it reaches the pterygoid. 

 The pituitary body and the infundibulum are now united. There is a distinctly 

 cartilaginous annulus tympanicus, as in the Batrachia ; the stapedial plate is distinct 

 from the bar of the columella, and the extrastapedial is discoid, and has a supra- 

 stapedial lobe, as in the Toad. The epipterygoid is not ossified, and is continuous with 

 the pedicle of the quadrate. The parietal fontanelle is wide open (PL X.). 



Seventh Stage. Nearly ripe. — The parietal fontanelle is now filled in, and almost 

 everything is in the same condition as in the adult, except that the synchondroses are 

 larger. The chondrocranium is largely ossified from the pituitary region, backwards, 

 but unossified in front. The epiotic has not coalesced with the superoccipital, and the 

 opisthotic has only ossified half the cartilage belonging to it. The notochord is flattened 

 in the occipital condyle, but is surrounded by a solid sheath of cartilage. Now, and for 

 a long time afterwards, there is no ossification of the articular cartilage, but its long plate 

 closely embraces it. The nasal capsules form two pouches, closed above and below, and 

 continuous with the septum nasi ; the preuasal rostrum is short and descending. There 

 is a distinct ethmo-palatine cartilage, and a rudiment of the inferior turbinal ; the epi- 

 pterygoid is ossified and segmented from the unossified pedicle of the quadrate ; the 

 quaclrate is ossifying, and is hollowed out to form the drum (Pis. XI.-XIIL). 



(ZOOL. CHALL. EXP. PART V. 1880.) E 7 



