158 Mr, T. Atthey on Anthracosaurus Riisselli. 



and nearly ^ inch in breadth ; it is small in proportion to the 

 size and strength of the jaw. 



The mandibular ramus of Anthracosamms consists of four 

 elements, viz. the dentary, the articular, the angular, and 

 the splenial. 



First, the dentary, bearing the teeth, is long and narrow, ex- 

 tending for nearly two thirds of the length of the ramus ; its 

 anterior end, which is attenuated, forms one half of the sym- 

 physis ; its posterior, much broader, joins with the articular 

 piece ; by its inferior edge it articulates with the splenial 

 posteriorly and with the angular anteriorly. Its surface is 

 covered all over with closely set and pointed tubercles. 



Second, the articular, the most massive piece of the ramus, 

 is united to the dentary in front ; from its upper margin arises 

 a low, rather rounded, coronoid process, and from its upper 

 and posterior part the articular process, bearing the glenoid 

 cavity for the reception of the condyle of the cranium. This 

 cavity is supported by the descending process, which forms the 

 posterior edge of the ramus, and articulates below by a broad 

 surface with the angular piece. The articular cavity faces 

 upwards and somewhat inwards and forwards ; it measures 

 2j inches in length, an inch in width, and -f^ inch in depth. 

 Its neck is strong and devoid of postarticular processes. 



Third, the angular. This, from its suture with the articu- 

 lar, extends along to the anterior end of the ramus, forming 

 its lower border and the remaining half of the symphysis. It 

 articulates by its upper edge with the splenial behind and at 

 about the middle of its length, and with the dentary in front. 



Fourth, the splenial. This lies along a great part of the 

 inner surface of the ramus, attached along the upper edge to 

 the articular and the dentary pieces ; below, both behind and 

 in front, it is connected with the angular, in conjunction with 

 which it forms two unequal elliptical openings, the anterior 

 much less than the posterior, which during life were filled by 

 membrane ; these openings are separated by a long obliquely 

 descending process of the splenial, which articulates with a 

 small upward projection of the angular : thus the splenial has 

 three connexions with the angular piece. 



The inner surface of the right ramus of the mandible is re- 

 presented in Plate X. fig. 1, one third of the natural size. 



It measures 16 inches in length,and,at4 inches in front of the 

 posterior margin, 4| inches in breadth. It bears 19 teeth, nearly 

 all of which are in a good state of preservation. The first in 

 front is \ an inch in length ; the second and third are a little 

 longer ; and the following thirteen are | inch, the last three being 

 somewhat shorter than that. 



