32 



like anterior tooth of the upper jaw, and not with the second of that series. 

 On the outside of the jaw, below the alveolar process, there is a shallow longitu- 

 dinal channel, and below this depression the horizontal ramus presents a sUght 

 but general convexity to its thick inferior border : the longitudinal course of 

 this border from the angle to the symphysis of the jaw is slightly sinuous, convex 

 in its posterior third, then gently concave, then very slightly convex below the 

 middle alveoli, and again very slightly concave where it begins to sweep inwards 

 to form the symphysis. This anterior termination is the most remarkable feature 

 of the lower jaw, and resembles the blade of a spade : it is inchned from below 

 upwards and forwards at an angle of 130° with the basal line, as a broad nearly 

 square plate of bone, diminishing in thickness to its upper margin, which is 

 nearly straight. The trenchant anterior edge is a little roughened or broken for 

 the attachment doubtless of a callous gum : it offers no trace of incisive sockets : 

 it forms a right angle with the lateral margins of the symphysis, which are 

 slightly concave ; each angle is rounded off. The inner surface of the symphysis 

 is smooth and concave at its anterior half, convex vertically at its lower half; but 

 here also smooth and without any ridge or process indicating attachments of 

 genio-hyoid or genio-glossal muscles. Its size, form and position strongly indi- 

 cate that it supported and facilitated the movements of a large and probably long 

 and prehensile muscular tongue. 



The outer surface of the symphysis is rough and irregular, slightly concave, 

 and with an oblique eminence on each side of the middle line. These eminences* 

 indicate the place of origin of the retractors of the lower lip. The lower margin 

 of the symphysis is almost trenchant and concave •, it is only one inch in advance 

 of the anterior socket. The lower margin of the horizontal ramus f expands to 

 form a thick convex support of the dental sockets, and again contracts to an 

 almost trenchant edge beneath the broad ascending ramus. 



The large elliptical entry to the dental canal is situated near the middle of the 

 inner concave surface of the ascending ramus ; a shallow depression leads for- 

 wards to it from below the inner overhanging part of the condyle. A narrower 

 and deeper groove is continued obliquely downwards and forwards from the pre- 

 ceding bed of the trunk of the dental nerve, and cuts through the middle of the 

 ridge bounding the general concavity of the ascending ramus. 



* Plate V. fig. 4. e, e. t Plate VI. fig. 3. 



