570 
ME. W. K. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 
thicker towards each end than in the middle, and only become bony in the ethmoidal 
region ( tr ., sjp.e.). Thus, in this respect, these bars correspond with their earliest con- 
dition in the other types ; in a larval Siredon less than half an inch in length they have 
a high crest ; and in Menobranchus , where they do not ossify, they are high, or crested. 
They are almost absolutely parallel from their prootic cup to their ethmoidal shaft- 
bone ; the appearance of inbending, at the middle, is due to attenuation of the bars. 
A little behind the inner nostrils (i.n.) the trabeculae gently turn inwards, and this 
inflected part is two fifths the length of the straight or interorbital part. 
But the great lower fontanelle is extended forwards to nearly the middle of the 
inflected tracts ; there the rods are ossified ; the rest is soft, and to the frontal wall are 
almost entirely confluent. 
This confluent part is a flat internasal cartilage (i.n.c.) ; it is wedge-shaped. Nearly 
the anterior third is notched, thus forming two short straight horns, the trabecular 
cornua ( c.tr .). 
Proximally, on the inflected part, there is on each side a free horn of cartilage ; it is 
gently arcuate, looking outwards and a little backwards ; this is the antorbital or ethmo- 
palatine element (e.jp a.). The internal nostril [i.n.) lies in the obtuse angle in front of 
this bar, and outside the ossified tract of the trabeculee ; its outer margin is a strong 
fibrous band or fascia. Inside this opening the ethmoidal bony tract of the trabecula 
is burrowed by the olfactory nerve (1). 
As in Menobranchus , there is no cartilaginous nasal roof; these types, therefore, 
correspond to very young Axolotls, and are below Siren and Menojpoma, the former 
possessing a small distinct nasal roof-cartilage, and the latter a very perfect cartilaginous 
capsule, with which the large antorbital cartilage coalesces*. 
The next cartilaginous element to be considered is the suspensorium, whose free 
segment is the mandible or, rather, its pith, the articulo-Meckelian rod. 
The direction of this arch and its pier is almost directly forward, as in the newly 
hatched Axolotl (Plate 23. figs. 1, 2, and Plate 22. fig. 3) and as in Batrachian larvae. 
Also, as in Batrachian larvae, the suspensorium has only one junctional process at its 
apex, the pedicle ( pd.), which is fused with the trabecula below where it is ensheathed 
by the prootic (fig. 7, tr., pd.)f. 
The “tuberculum” of this bar, the otic process (ot.pt.), is a remarkably slender, free, 
digitiform outgrowth ; it passes obliquely over the front and outer face of the ear- 
capsule, the portio dura (7 2 ) emerging beneath its middle. 
The only sign of a pterygoid process is in the rather suddenly convex outline of the 
flat fore margin of the upper, unossified part of the suspensorium. The lower half is a 
very solid but compressed mass, ossified save at the scooped articular face ; its inner side 
has the styloid end of the osteo-pterygoid process attached to it (q., ppt.g.). 
* Wiedeesheim (op. tit. plate 1. fig. 1, N.K.) figures the skull of Menobranchus with a fenestrate nasal 
cartilage. 
t In the abstract of my second paper on the Batrachian Skull (Proc. Eoy. Soc. No. 165, 1875, p. 141) it is said 
that the ascending process only is present ; this is a mistake. 
