OF THE SKULL IN THE AMPHIBIA UEODELA. 171 



beneath the fore and the hind brain. This space is called pituitary ; but the pituitary 

 body only occupies a foot breadth at the end of this great field. This main basal 

 fontanelle is followed by another, the " posterior basicranial fontanelle " of Rathke. 

 This is formed by a reopening of the original membranous space on each side of the 

 notochord, between the ends of the trabecular and the apices or fore ends of the para- 

 chordals. 



The cranial notochord is still large; it is bounded in front by the trabecular, and 

 behind it lies on the basal plate ; it fills the space between the occipital condyles, as it 

 emerges to become the axis of the spinal column (fig. 2, nc, oc.c). 



The occipital arch has become bony, all but the mid line, above and below (e.o,f.m). 

 This bony tract stretches over the epiotic and opisthotic region of the auditory capsule. 



Scarcely distinct from this tract below is another (pro) which runs in a crescentic 

 manner as two wings of bone, one on the antero-inferior, and the other on the antero- 

 superior face of the auditory capsule. Thus the " sacculus " of the fenestrate region is 

 still floored with cartilage : a band of cartilage also intervenes between the epiotic and 

 prootic bony tracts, and along the actual front face of the capsule ; this latter tract has 

 a plaster of cartilage upon it, derived from the basal plate, and this generally remains 

 soft in relation to the suspensorial pedicle. The fenestra ovalis is now perfect, and is filled 

 with a thickish cartilaginous stapes (fig. 6, st). The skull in front of the car-sacs is 

 entirely unossified, yet there has appeared a bony plate on each side, which in osseous 

 fishes is an ectostosis. This is the prefrontal or ectethmoid (e.eth). 



The sphenoidal walls of the trabecular (tr) are more perfect, but scarcely overlap 

 above, so that the fontanelle is complete. In front the nasal roofs (na) are of great 

 extent, and they are quite confluent with the very wide trabecular cornua. The ethmo- 

 palatine cartilages (fig. 6, outside p>a) have also united themselves to the posterior edge 

 of the nasal curtain. 



Other most instructive characters have now appeared : the internasal plate (in.c) has 

 lost its hinder projection and has gained one in front ; this is the prenasal rostrum (p.n), 

 a process not common in the Urodeles, and suppressed in many of the Anura. In the 

 latter group the primary cornua trabecular give off a small process, the " prorhinal ;" it 

 is a secondary cornu : this is fairly seen in the ripe young of the Salamander (fig. 6, c.tr), 

 and will persist in the adult (PI. XVI.). The rest of each cornu forms the subnasal 

 lamina, or trabecular floor of the nose, as in the Frog. 



The large suspensorial cartilage is still only confluent with the skull by its ascending 

 process (a.p) over the first branch of the fifth nerve; the " pedicle " proper is never more 

 than a bulging of the lower face of the ascending process in this species. The otic 

 process (otp) is well developed, and clings by its expanded face to the most projecting 

 part of the ear-sac. A pterygoid process (e.pg) has appeared. 



The quadrate region of the suspensorium is now largely ossified (q), as is the rule in 

 the tailed Amphibia, and the exception in the Anura ; the condyle still looks forwards, 

 and reaches to an imaginary line across the middle of the skull. 



Thus we see that, including the quadrate bones, there arc only three pairs of osseous 

 centres found, as yet, in the substance of the chondrocranium. 



