280 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



front, and the ex-occipitals behind, whilst externally they are hidden by the large ossa 

 quadrata — the proximal hsemal elements of their own sclerotome, of which they are, if 

 Professor Goodsir be right, the inferior neurapophyses : Professor Huxley prefers calling 

 them, as well as the contiguous mastoids and epiotics, ' periotic bones.' The determina- 

 tion of the petrosal in the different classes of Vertebrata seems to Professor Huxley and to 

 the writer to be a very straightforward and simple piece of work ; but its bibhography is 

 frightful ; and although the form, functions, and relations of this element speak one 

 language, its very existence has often been ignored when well developed, as it is almost 

 invariably, whilst the somewhat inconstant ' mastoid ' has been often mistaken for it. 



That the exit of the main nerves can be depended upon for the determination of 

 special homologies there can be but little doubt (see Huxley, Croon. Lect. p. 36) : to 

 us, the denial of this is the weakest point in one of the most masterly disquisitions on the 

 subject of homologies we have ever had the pleasure and the advantage to read (see 

 Professor Goodsir, op. cit. p. 171). 



Basi-temporal (Parker). (PI. LXV. figs. 3 & 7, & t.) 

 Above the petrous bone is the squamosal, and below it we have what might be the broad 

 centrum of the ' temporal sclerotome ' of Goodsir. In describing the basi-occipital, elegant 

 crescentic laminae, the pterapophyses (confluent in front) of the basi-temporal, were 

 spoken of. This thin, free, horizontal margin of the base of the skull in the temporal 

 region surrounds a semicircular mass of bone, the round border of which is in front, 

 its mesial part is concave, and its sides thick, mammillate, and somewhat ridged trans; 

 versely. These elevated tubercular masses are each one-tliird the width of the thick 

 part of this bony base, the middle third being elegantly concave. This concave part 

 alone lies in the same plane as the basi-occipital ; the two original halves of this, the 

 basi-tempox'al, being cortical ossifications of the original cartilaginous basis cranii. We 

 have already said that the alar margins of this basi-temporal are confluent with the par- 

 occipital alee by the bridge of bone which forms the large lateral reniform foramen. 

 These alar productions form the floor of the tympanic cavity, and are evidently the 

 actual homologues of a pair of 'pterapophyses,' which are very largely developed in 

 certain lissencephalous mammals, e.g. the Mole and the Hedgehog. In the latter 

 animal the tympanies are mere osseous rings (these bones becoming fainter as we ap- 

 proach the O vipara) ; but the internal and inferior part of the tympanic cavity is all formed 

 by supplementary 'pterygoid plates,' which encroachupon the basi-occipital region, and 

 have between them, in front of the basi-occipital, a large dome-shaped recess. Professor 

 Owen's elegant term ' pterapophysis ' is very convenient for these productions of the 

 cranial centra — the analogues of the vertebral parapophyses and hypapophyses (pro- 

 cesses that run insensibly into one another). 



Now it is evident that these temporal pterapophyses of the Hedgehog are something 

 supplementary, for they are a line and a half behind the pterygoid bones and the 



