EAELY GROWTH OR THE BONES OE THE HUMAN RACE. 
171 
nized as the mylo-hyoidean ridge, the posterior extremity of which is turned upwards 
and outwards to join the inner surface of the ascending ramus, and thus forms the inferior 
dental foramen, whilst the shallow groove beneath this ridge is occupied by the remains 
of the cartilage of Meckel (Plate XIII. fig. 8, d and b). 
The extremity of Meckel’s cartilage is ossifying in a foetus 2‘3 to form the inner tri- 
angular block of bone (below the anterior part of the ridge) which determines the size 
and shape of the lower anterior portion of each half of the jaw, beneath, that is to 
say, the incisor sockets (Plate XIII. figs. 6 (3), 7, & 8). To the twist acquired in this 
portion of the bone the prominence of the front of the maxilla, known as the mentum, 
or chin, appears to be due. In a foetus 3'5 the cartilage is ossified as far back as the 
junction of the middle with the anterior third of the body of the bone ; behind this 
point it gradually shrinks during the subsequent growth of the ramus. In a foetus 4‘7 
the block of bone formed in the anterior extremity of the cartilage of Meckel is still 
clearly defined. 
Explanation of the Plates. 
PLATE XIII. 
Pig. 1. Part of human foetus (four-tenths of an inch long): a , plates for ethmoid and 
turbinate cartilages ; b , maxillary lobe prolonged towards the middle line to 
form the palate (3 linear). 
Eig. 2. The same as the preceding : «, plates for ethmoid and turbinate cartilages ; 
b , maxillary lobe showing its irregular inner surface ; c, frontal-nasal process 
turned back to expose the nodules on its under surface and the continuation 
of the ethmoid plates. 
Eig. 3. Part of superior maxilla from foetal Pig (2 inches long) : a, process in the situa- 
tion of the human incisor portion (5 .linear). 
Fig. 4. Vomer of human foetus (2-3 inches long): a, anterior extremity of the bone 
(15 linear). 
Fig. 5. Part of skull of mammary foetus of Kangaroo (2 inches long) : a, process in the 
situation of the human incisor portion (3'5 linear). 
Fig. 6. (1) Outer surface of left inferior maxilla from human foetus (1 inch and five- 
tenths long) : the mental extremity is sharply bevelled off below ; the situa- 
tion of the mental foramen is indicated. (2) Anterior extremity of Meckel’s 
cartilage and a layer of membrane lying beneath it, from the same foetus. 
(3) Eight inferior maxilla, inner surface, from human foetus (2‘3 inches long) : 
a, ossified anterior extremity of Meckel’s cartilage ; b, plate of bone overlying 
the groove for the cartilage and separating it from that for the dental nerve 
(3’5 linear). 
Fig. 7. Left inferior maxilla, inner surface, from human foetus (3 - 5 inches long) : a and 
b refer to the same structures as in the last figure ; c points to the convex 
upper surface of the plate of bone bounding the dental canal (3-5 linear). 
MDCCCLXIX. 2 A 
