330 REPORT— 1873. 



Archegosaurus the elements of the occipital segment proper may have been 

 persistently cartilaginous, except so far as they were encroached upon by the 

 supraoccipital and parasphenoid ossifications. The condyles were most 

 probably entirely cartilaginous. Professor Owen* supposes that " the head 

 was connected by ligament, as in Protopteri, to the vertebral column of the 

 trunk, and chiefly by the basioccipital part." 



The existence of two lateral occipital condyles in this order is a feature of 

 great morphological importance and zoological value. If, as Yon Meyer and 

 many other writers have supposed, the Labyrinthodonts are tnie ReptUia, they 

 constitute the one exception to the rule that in each of the four higher classes 

 of Vertebrata the number of occipital condyles is constant. 



The Parasphenoid (sphenoideum of Von Meyer t and BurmeisterJ). — In 

 Trematosaurus a large undivided bone underlies the base of the cranium, 

 giving off on either side a postero-lateral process which joins the suspensorial 

 peduncle. In front it passes into a rostrum or processus culfriformis, which 

 separates the palatine foramina, and articulates in front with the vomers. 

 Between the postero-lateral and the cultriform processes there is on each side 

 a broad outstanding extension of the parasphenoid, which joins the pterygoid, 

 and, together with that bone, separates the palatine foramen from the palato- 

 temporal fossa§. Burmeister describes lateral ascending processes of the 

 bone as passing upwards to join the margins of the parietals on the under- 

 side of the cranial roof and extending forwards to about the level of the 

 parietal foramen ||. The parasphenoid of Mastodonsaurus has in general the 

 same form and relations. 



In Archegosaurus a similar bone is found, but so displaced that its con- 

 nexions cannot be accurately made out. It is of spatulate form — the posterior 

 end being dilated and of rounded triangular or polygonal outline, whUe the 

 anterior end is extended into a long slender processus cultriformis. The ex- 

 panded end is often displaced backwards so as to project beyond the base of 

 the skull. The connexions of this bone with the pterygoid are shown in one 

 of the examples figured by Von Meyer %. Its position with respect to the 

 palatine foramen and the palato-temporal fossa appears to have been much 

 the same as in Trematosaurus ; but there is no trace of any postero-lateral 

 process given off to join the quadrate. That bone has not, indeed, been 

 identified in any specimen of Archegosaurus ; nor is the mandibular articula- 

 tion known in this genus**. The fore part of the parasphenoid of Anthraco- 

 saurus is known ft. It agrees in aU essential point* with that of Archegosaurus. 

 Prof. Owen has figured a detached parasphenoid of Dendrerpeton associated 

 with other bones ; but no mention is made of it in the text JJ. 



In Loxomma the upper surface of the parasphenoid has been examined. 

 About an inch in advance of the spheuo-occipital suture are two broken 

 processes g of an inch apart, which are directed towards the parietal bones. 

 Again in advance is a strong median ridge, extending as far as the anterior 

 third of the palatine foramen, which may have supported an interorbital 

 septum. , 



There is no ground for doubting that this element of the Labyrinthodont 



* Comp. Anat. of Vertebrates, vol. i. p. 85. 



t Reptilian aus der Steinkohlenformation, p. 19. J Trematosaurus, p. 29. 



§ Burmeister, Trematosaurus, § 14. |{ Loc. cit. p. 30. 



'\\ Reptilien aus der Steinkoblenformation, t. v. fig. 7. 



** The parasphenoid of^rc7^egro,'!«^<r^(s is described by Von Meyer, 'Reptilien' &c., p. 19. 

 ft H\isley, " Description of Anthracosaurics Russelli," Quart. Journ. Geol. Soc. vol. six. 

 p. 56 (1863). 

 \\ Quart. Journ. Geol. Soc. vol. ix. p. 58 (1853); see also pi. ii. fig. 2. 



