1903.] ON THE VERTERR® OF THERIODONTS. Lie 
3. On the Axis, Atlas, and-Proatlas in the Higher 
Theriodonts. By R. Broom, M.D., B.Se., C.M.Z.8. 
[Received January 20, 1903. } 
(Plate XVIIL.') 
Hitherto, though something has been known of the structure 
of the axisin at least two of the Dicynodonts and in Cynognathus, 
we have been practically ignorant of the structure of the atlas in 
any of the Theriodonts or Anomodonts. In fact, Prof. Seeley (1) 
in describing the axis of Cynognathus, seems to be in doubt 
whether he is really dealing with an axis, or with an axis and 
atlas combined. On page 100 of his paper he says, ‘The first 
vertebra appears to be anchylosed to the second”; while a little 
further on he states that “this vertebra is remarkable for its 
form being exactly like the odontoid process of the vertebra in 
many animals, and suggesting the idea that the atlas is lost” ; 
and in a note he adds: ‘ This appears to be confirmed by the sub- 
sequently to be described condition in Z'ropidostoma dunni.” In 
counting the vertebra, however, he counts the axis as the Ist 
cervical, and states that “there are 6 cervicals.” Gadow (2), in 
his recently published work on Reptiles, possibly misled by Seeley, 
definitely states that “the atlas is fused with the axis.” Con- 
sidermg how mammal-like the higher Theriodonts are, and that 
the axis bears a very marked resemblance to the mammalian axis, 
having a large spime and a well-developed odontoid process, it 
seems remarkable that the idea should have arisen that the atlas 
was anchylosed to the axis, more especially as there is no part 
of the axis in Cynognathus that bears any resemblance to any 
kniown atlas. 
When in Grahamstown recently, I had an opportunity, through 
the kindness of Dr. Schonland, of examining the Theriodonts in 
the Albany Museum, and especially the very fine specimens of 
Gomphognathus and Trirachodon, which have been described by 
Seeley (3), and which have been so marvellously developed under 
his direction. In both the type specimens of Gomphognathus 
kannemeyert and Trirachodon kannemeyeri the anterior cervical 
vertebra are most beautifully shown, but Seeley in his description 
ot the specimens makes no reference to this most important 
region, beyond stating (p. 53) that “ the occipital plate [in 7’rira- 
chodon]| is not completely exposed owing to some of the vertebre 
being in contact.” Twoof his figures of the skull of 7'rivachodon 
show the atlas and part of the axis; but as no distinction is shown 
between matrix and bone, it is difficult to make anything of the 
drawing. 
The beautiful specimen which forms the type of Gomphognathus 
1 For explanation of the Plate, see p, 180. 
Proc. Zoou. Soc.—1903, Vou. I, No. XII. 12 
