96 OSTEOLOGY [Parr II. 
its lower edge. A large vascular canal perforates the dentary very obliquely, running forward from the 
dental space; it opens externally nearer the upper than the lower border, about nine lines behind the 
symphysis, and passes into a deep groove, which, advancing towards the core, is concealed anteriorly 
by the perforated and undermined, posterior crenate edge of the latter, as it ascends obliquely backwards : its 
outer wall is pierced by two foramina, opening behind into a furrow, which disappears halfway to the dentary 
notch. ‘The dental canal terminates, internally, above the anterior extremity of the opercular; the orifice is 
subdivided by a small process of the latter; a rough depressed triangular tract is continued forwards from 
it, to the thick posterior sub-vertical border of the symphysis, which is perforated horizontally by a vascular 
canal, emerging close to its lower edge, and midway between its angles; the mentary groove, already 
mentioned, joins this canal at its centre ; externally, a series of five large apertures open upwards from it ; 
three or four downwards, and one on the rough concave symphysial surface. 
The fissure between the angular and articular pieces, is concealed by the dentary without, and the oper- 
cular within; that between the thin lamina of the surangular and the tumid rostrum of the articular 
element, is converted by the dentary fork into an elongated elliptical foramen, six lines and a half long, 
and one line and a half deep, its anterior angle corresponding to the posterior orifice of the dental space. 
The posterior segment of the ramus increases in breadth as it retrogrades, and chiefly inwards in its hinder 
moiety, so as to present a large pyramidal internal angle; while the external is produced backwards into a 
compressed semi-lunar plate, with a thick and rough projecting edge, passing below into the smooth crest 
running upwards and inwards, between the basal facet, and the anterior aspect of the inner angle, which 
slopes obliquely forwards and outwards and passes into the imner surface of the ramus. 
The basal or digastric facet is triangular, with the rough obtuse apex internal; the subconcave pitted 
surface passes externally into the inner convex aspect of the angular plate. 
The complex articular surface is transversely oblong; without, it presents a longitudinal, slightly 
concave, reniform tract, with an external convex border; which plays on the outer flattened segment of the 
tympanic mandibular surface: within, it is deeply excavated for the reception of the ridge-hke inner condyle; 
the concavity is directed inwards and forwards, becoming wider and shallower, its anterior depressed edge 
descending, while the posterior rises internally into a rough projection, rendering it concave transversely ; 
this edge is narrow, rounded without, but internally, it presents the large oval pneumatic aperture. Synovial 
cartilage lines the inner half of its floor and its anterior surface, detaching a tract to line the reniform concavity. 
The low short coronoid process is separated by an interval of six lines and a half from the 
articular surface, and corresponds to the junction of the four anterior fifths with the posterior; the upper 
edge of the surangular, anterior to it, is smooth and rounded. 
An elongated tubercle extends downwards and forwards from the centre of the outer projecting border of the 
external segment of the articular surface, and its anterior angle is prolonged into a ridge, passing forwards to 
the extremity of the lower dentary limb. The outer surface of the posterior segment is thus divided 
diagonally, into two subequal surfaces; the posterior of which is triangular, most concave, and deeply 
pitted; it gives attachment to the muscles of the tongue, while the anterior furnishes insertion to the 
M. temporalis. 
The pitted surface on the inner aspect of the jaw, for the attachment of the JZ. pterygoideus 
internus is defined anteriorly by an oblique irregular ridge, commencing at the upper edge a little anterior to 
the articular surface, and descending obliquely forwards to a groove, directed obliquely inwards and forwards, 
across the lower edge of the angular, from the extremity of the dentary to that of the opercular; it extends 
backwards on the anterior aspect of the imner angle. 
The deeply concave pitted tract for the insertion of the erternal pterygoid, is anterior and superior 
