142 



coronoid piece. The numbers indicate the names of the bones according to 

 the Table of SYNONYMS. Hunterian. 



661. A superior maxillary bone and one ramus of the lower jaw of the Cyclodus. 



This and the specimens Nos. 656 and 680, show extremes of modification in 

 the form of the teeth, with the same mode of attachment and development 

 of those parts. 



Family Geckotia. 

 Genus Rhynchocephalus. 



662. The five first vertebrae of the trunk of a Lacertian (Rhynchocephaluis). 



The atlas consists chiefly of the hypapophysis and neurapophyses ; the former is in the 

 form of a transverse arched bar, concave upwards, with the anterior border cut obliquely to 

 receive the under part of the occipital condyle ; the posterior border is convex vertically, and 

 adapted to the transverse trochlear groove in the fore part of the odontoid process ; the neur- 

 apophyses have a small articular surface at the fore part of their base for the occipital con- 

 dyle, and a second at their inner and back part for their proper centrum, the odontoid process. 

 They are expanded superiorly, develope a small posterior zygapophysis, exterior to which 

 is a tubercle ; and they come in contact, but do not coalesce, above the neural canal. 



The odontoid process has coalesced with the body of the axis, which it equals in height and 

 exceeds in breadth : it is convex from side to side, concave vertically at its lower half, having, 

 as it were, a channel scooped out from side to side : this land of joint will allow of great extent 

 and freedom of motion of the atlas with the head from side to side ; whilst the vertical move- 

 ments would be restricted. The neurapophyses of the axis have coalesced with the centrum 

 below, and with each other above, where they develope a strong ridge or spine, which is most 

 produced in the antero-posterior direction. An autogenous hypapophysis is wedged into the 

 inferior interspace between the centrum of the axis and the third vertebra. The centrum and 

 neurapophyses of the third vertebra have coalesced : a short diapophysis projects from the line 

 of union. The anterior and posterior zygapophyses form the angles of the broad base of the 

 neural spine : this spine is of moderate length, thick and trihedral. There is a small wedge- 

 shaped hypapophysis beneath the interspace of the third and fourth vertebrae. The fourth 

 vertebra has a short pleurapophysis on each side, with a bifurcate proximal end articulated by 

 a broad tubercle to the diapophysis and by a slender neck and head to a rudimental parapo- 

 physis, but this is very feebly marked off from the diapophysis. In the fifth vertebra the 

 parapophysis and diapophysis form together an oblique ridge, chiefly extended vertically, and 

 to which the expanded head of the pleurapophysis articulates by a single surface. There is a 

 wedge-shaped hypapophysis at the interspace of the fourth and fifth vertebrae : both ante- 

 rior and posterior surfaces of the centrum are excavated by a deep conical cavity. 



Presented by Prof. Owen, F.B.S. 



