1888.] ANATOMY OF THE MESOSUCHIA. 423 



brae speaks distinctly in favourof its diapophysial character. The 

 common acceptance of the pair of atlantal styles as riblets seems, 

 then, well founded. 



The origin of the ribs in connection with the myocommata, their 

 primitive independence of the permanent vertebrae, and their inter- 

 vertebral position as regards the latter suggest the inquiry whether 

 instances of ribs being borne on intercenira are known. 



It has been thought that an affirmative answer to this is to be 

 found in the vertebral column of RhachitomidtE (E. D. Cope). In 

 support of this Dr. G. Baur (26) cites Prof. E. D. Cope, who describes 

 the capitellum of the furcate rib of a Pelycosaurian — Embolophorus 

 fritUlus — as being borne on an " intercentrum" (27), But the 

 significance of this turns on the true morphology of the part here 

 termed " intercentrum " by Cope. Now in stating the generic 

 characters of Trimerorhachis this author writes : — " The centrum is 

 represented by three cortical ossifications of the chorda sheath, a 

 median inferior, and two lateral. The lateral pieces are quite dis- 

 tinct from one another, and are in contact with the neurapophyses 

 above, and the posterior border of the median segment in front. 

 The neural arch joins chiefly the lateral elements, but is in slight 

 contact with the lateral summits of the inferior element." " The 

 median element I call intercentrum" (27). Again, referring to 

 Rhachitomus valens, this author states : " Each vertebra consists of 

 two segments, an intercentrum and a neural arch. The true centrum 

 is wanting in the specimens at my disposal, and the intercentr.im 

 supports portions of two adjacent neural arches. With these it 

 shares the intervertebral articular face usually borne by the centrum " 

 (28). It is evident from these passages that Cope's " intercentrum " 

 (as is mentioned in an earlier part of his paper) is Gaudry's "hypo- 

 centrum.^' Again, in E. D. Cope's definition of the Gariocephala 

 the following statement occurs: — "Vertebrae consisting of centra 

 and intercentra, the former not extending to the base of the vertebra, 

 the latter not rising to the neural canal. Tlie centrum consisting of 

 two parts distinct from the superior neural arch, viz. a lateral piece 

 on each side " (29). Here centrum is used not as equivalent to 

 body, for this latter term in its general application comprises also 

 the inferior piece. It would appear that Cope's application of the 

 term centrum to the inferior piece was consequent on his interpre- 

 tation of the pair of lateral pieces (Gaudry's pleurocentra) as com- 

 posing the centrum. I do not gather from any of his writings that 

 Prof. Cope has, in any of the Ganocephala described by him, found 

 intercalary pieces concurrently with vertebral bodies of the con- 

 struction just mentioned, and the argument based on his obser- 

 vations in relation to this subject, viz. Gaudry's hypocentrum is an 

 intercentrum, is not, I submit, conclusive ; and, this being so, the 

 inference drawn from the supposed costal articulation with the 

 intercentrum in Tj-imerorkachis, viz. that the atlantal basilar piece 

 is really an intercentrum, appears to me to want confirmation. Lower 

 in the vertebrate scale instances are known, of which Sjyatularia is 

 an example, where, together with vertebrae consisting of a neural 



