236 REPORT— 1873. 



pensorium in great part, but may have fiirnislied points of origin to some of 

 the mandibular muscles. 



The relations of the quadrate and quadrato-jugal have not been determined 

 accurately ; but there is little chance of error in supposing that the quadrato- 

 jugal represents a membrane-bone investing the mandibular suspensorium, of 

 which the quadrate, when jiresent, constitutes the ossified part. In some cases 

 at least (Masfodonsaunis, ArcJiegosaurus, Trematosaurus) the quadrato-jugal 

 furnishes the outermost part of the articular surface for the mandible. 



The Quculrate. — The quadrate of the Labyrinthodonts is as j^et very imper- 

 fectly known. In Trematosaurus, which has yielded the best materials for exa- 

 mination, it is described by Burmeister* as generally similar to the quadrate 

 of the Crocodile, and as contributing the two inner of three rounded depending 

 ridges for the articiilation of the mandible, the quadrato-jugal supplying the 

 outermost. No other important details have been distinctly made out. 



In Micropholis " the articular end, -^-^ of an inch broad, and flattened from 

 above downwards, exhibits a cond^doid surface, which is divided hy a groove 

 into a stronger internal and a less prominent external portion. In front of 

 the condyles the quadratum is very thin, but it rapidly expands so as to cover 

 all that remains of the flat lateral face of the suspensorium, and extends 

 forward to about midway between the articular condyle for the mandible and 

 the posterior margin of the orbit. At this point the bony matter disappears "f. 



The suspensorium has a downward and backward direction, as in the adult 

 Batrachia. It probably remained more or less cartilaginous in many of the 

 Carboniferous species, as in most recent Amphibia. 



Tlie Mandible. — The rami of the mandible are long and straight, of con- 

 siderable vertical extent near the condyle, and gradually tapering forwards. 

 The upper and lower edges are nearly straight ; but in some genera there is a 

 low coronoid process, which rises as an elongated triangle from the upper 

 border, sloping very gradually in front, but rather more rapidly behind. 



Each ramus is made up of three elements f ; (I) a dentary bone, which 

 receives the teeth, and, in some cases, constitutes tlie upper half of the ramus 

 throughout the greater part of its length ; (2) an angular piece, which forms 

 the slightly marked angle of the mandible, and is continued forwards along 

 the lower border, both on the inner and outer side, to near the sympliysis, 

 supporting the dcntaiy bone by a groove upon its iipper edge. The angular 

 bone is usually ornamented with a strong sculpture, radiating from the angle 

 itself. The articular element (3) comprises the condyle and the upper part 

 of the posterior end of the ramus. Its structure, as revealed by a fine 

 example of the mandible of Anthracosaurus, is thus described by Jfessrs. 

 Hancock and Atthey : — " The articular piece stands well up ; the neck is 

 short and stout ; the process bearing the glenoid surface is massive, and is 

 transversely elongated, measuring two inches and a quarter long, and an inch 

 wide ; the glenoid cavity is deep, and takes a slight sigmoid curve ; behind 

 at the outer margin there ha» been a stout projecting process ; and in front 

 towards the inner margin there has been a similar projection of the Hp of the 

 articular cavity. It would therefore seem evident that the attachment of the 

 mandible to the tympanic trochlea must have been very firm, rendering the 

 movements of the jaw secure and precise " §. The glenoid cavity of Loxomma 

 is described by the same authors as " transversely elongated, deep, and con- 

 siderably elevated" ||. It has no postarticular process. 



* Trematosaurus, pp. 28, 29. t Huxley, ' Quart. Journ. Geol. Soc' vol. xv. p. 650 ClSog). 

 X See p. 226. ' 



§ Nat. Hist. Trans. Northumberland and Durham, vol. iv. p. oSSI. || Ibid. p. 392. 



