DEVELOPJIENT OP TILE SKULL IN THE UEODELES. 183 



B. The Undocranium of Menopoma. 



Much of the inner skull can be traced from the outside, where it is not fairly covered 

 by the outer bony plates ; for a further elucidation of it the reader is referred to the 

 similar skull of the larva of Triton (PI. XL.). 



The foramen magnum (PI. XXXVIII. fig. l,f.ni) is superior, triangular, and small; 

 the occipital condyles {oc. c) are subpedunculate, large, wide apart, and oblique ; their 

 direction is inwards, downwards, and forwards, and their form oval. 



The exoccipitals (e.o) can be seen to be distinct from the prootics {jjr.o) ; they form 

 the sides of the hourglass-shaped hind skull. In front, below, they reach almost to the 

 foramen ovale {vh,st) ; above, they overlie it; below, on their sides, they are perforated 

 for the ninth and tenth nerves (ix, x). 



Between them, behind, there is a shallow transversely oval cup of cartilage, floored 

 by the parasphenoid ; this is for the odontoid rudiment of the first vertebra. 



Outside the parasphenoid, below, the vestibule is exposed ; and in the middle region 

 the capsule is unossified; there is the large fenestra ovalis outside, with the compound 

 columella {p.luj, st), and a little further forward the passage for the facial nerve 

 (vii); this nerve is seen riding over the columella; the stapedial portion of this organ 

 is an oval disk of bone [st) with a cup-like process for the stem or " medio-stapedial." 



Above (fig. 1, pr.o) the prootic is exposed in the postorbital region ; it crops up in 

 front of the temporal part of the parietal, and of the head of the squamosal [p.sci) ; it 

 bounds the foramen ovale (v) inside and behind. 



The fontanelle is covered above ; and the great basal membranous space is floored 

 below ; the sides of the endocranium formed by the trabeculse are exposed above, all 

 along the orbital region, and below, between the parasphenoid and pterygoid in front. 



Most of this basilateral tract is ossified as the " sijhenethmoid " [sp.e). It is separated 

 from the prootic, behind, by the ascending process [a.p); and in front it reaches to the 

 ethmo-palatine {e.pa). 



At its hinder third this bone is perforated and grooved by the optic nerve (ii), which 

 also forms a channel in the pterygoid. The unossified cornua trabeculee are very broad ; 

 they and their internasal conjugation are hidden by the investing bones^ 



The nasal roofs {na) are very large and wide ; and they have a considerable pyriform 

 tract uncovered behind the nostrils (e.n), and appear, above, in the angular space 

 between the prefrontals and maxillaries. 



Below (fig. 2, /. n) the inner nostrils are seen to be very large, oval, oblique spaces, 

 seven or eight times as large as the outer. 



c. The Lower Arches of the Menopome. 



Behind the nasal roof, and confluent with it externally, and then separated by a 



* Wiedersheira {op. cit. pi. ii. figs. 24, 25) shows that the Largo hollow nasal pouches are quite confluent 

 with the cornua trabeculae ; in front there is a large round notch of greater extent than the confluent part. 



