22 PROF. HUXLEY ON THE SPECIFIC AND GENERIC 



sides of the scute seem to meet in an angle. This may be called 

 the ' angulation ' of the scute. From before backwards, the inner 

 surface of the scute is a little convex. The scute is thickest in the 

 middle ; posteriorly, it thins off to an edge and overlaps its suc- 

 cessor ; anteriorly, its outer surface is bevelled off at an acute angle 

 with the inner, so as to give rise to a smooth shelving surface — 

 wide from side to side, narrow from before backwards — forming the 

 ' articular facet,' which is overlapped by the inner surface of the 

 posterior edge of the preceding scute. I have termed this the 

 * articular facet ;' but it must not be supposed that there is any- 

 thing like a true joint between the opposed facets of the overlap- 

 ping and overlapped scutes ; on the contrary, they are at once 

 separated and connected by the dermal connective tissue. 



The posterior margin of the articular facet is separated by a 

 deep transverse groove, divided by little partitions into as many pits, 

 from the rest of the sculptured surface ; but there is no trace of 

 any suture dividing the scute into two portions. The lateral 

 margins of each scute are united by serrated sutural edges w ith 

 those which lie next to them in the same transverse row ; so that 

 each row forms a nearly solid flat bony bar, composed, in the mid- 

 dle of the back, of as many as ten distinct scutes. The outer edges 

 of the outermost scutes only, thin off and exhibit no sutural ser- 

 ration, inasmuch as they are not directly connected with any other 

 scutes. 



The median line of the back corresponds in general with the 

 suture between the two middle scutes of each transverse row; so 

 that the scutes are disposed symmetrically on either side of that 

 line. Furthermore, the anterior part of the inner surface of each 

 of the two middle scutes is connected by ligament with the extre- 

 mity of the spinous process of a vertebra ; at least, this is the 

 case in the dorsal, lumbar, sacral, and anterior caudal regions. 



The scutes which protect the ventral side of the body, from 

 the throat backwards, are four-sided and similar in their orna- 

 mentation to the dorsal scutes ; but they exhibit neither ridge nor 

 angulation, their outer and inner surfaces being parallel, and either 

 nearly flat or evenly curved. Each forms, in fact, a segment of a 

 large cylinder, inasmuch as the whole ventral shield is convex 

 transversely, being nearly flat in the middle and much bent up at 

 the sides. The dorsal shield, taken as a whole, is, on the contrary, 

 nearly flat. The lateral edges of the ventral scutes interlock 

 suturally ; and their anterior and posterior edges are overlapped 

 and overlap, just like the dorsal scutes. The outer edges of the 



