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MR. GEORGE W. CALLENDER ON TLIE FORMATION OE 
The subaxial arches below the mandibular are the fourth, or lingual ; the fifth, or 
hyoid ; the sixth, or laryngeal ; and the seventh, which, differing from the preceding in 
its relation to the notochord, may be named the exoccipital or shoulder-girdle. There 
is also an imperfect arch connected with the laryngeal which will be described with it. 
The changes which will be described as occurring in the formation of these structures 
take place between the fifth and twelfth weeks of foetal life (30th to 84th day)*. 
The Fourth Subaxial Arch — the Lingual. 
In a foetus less than ‘4 of an inch in length this arch is recognized as a small bud-like 
process below the mandibularf ; in a foetus measuring ’45 this bud has grown out to the 
middle line, and has joined its fellow below the mandible (Plate I. fig. 1, 1). The man- 
dible, rather less than T8 from side to side and -03 deep, is yet membranous, and is 
closely connected by its lower border with the lingual arch ; but in the midst of the 
connecting membrane two distinct lines of dense tissue are distinctly traced, meeting in 
the middle line. On either side of this they swell up into a pointed mass, and here the 
tongue is rapidly formed ; so rapidly, indeed, that whilst in a foetus of # 45 its position 
is indicated only by an ill-defined thickening of the tissue above the centre of the arch, 
in another foetus of '55 it is seen completely formed. From the eighth to the ninth 
week (foetus ‘9) the lingual arch, distinct from the hyoid, grows into a rounded cord 
which begins to contain cartilage. It is attached by a globular head to the cartilage for 
the internal ear below and behind the root of Meckel’s cartilage ; its anterior extremity 
descends to the next lower arch, becomes slightly swollen, and loses its distinct character 
in the structures passing into the base of the tongue ; so that in a foetus of 1*2 this extre- 
mity is no longer recognized, although the rising of its tissue into the root of the tongue 
is still traceable (Plate I. fig. 2, l , fig. 3, l). The lower border is now, by the anterior 
extremity, in close relationship with the upper surface of the hyoid and contains carti- 
lage, the future lesser horn of the hyoid bone. 
At this stage, ninth to tenth week, the connexion of this arch with the cartilage at the 
base of the skull is as follows : the globular head is still distinct, and seems partially cut 
off' from the basal cartilage (Plate I. fig. 3, 1 1). From this point, for *05 of an inch 
forward, the rod is formed of cartilage ; the remainder ('07 long), except the extreme 
anterior portion already spoken of, is a dense membrane. In the opposite direction 
(Plate I. fig. 3, 1 1 to l ll) there is continued from the rod a ridge of membrane, lying 
on and becoming identified with the cartilage of the base ; and this, after ascending for 
•05 of an inch, turns forward and is continuous with membrane, a descending spur from 
which forms a distinct ring, which extends to that in which the squamous and zygomatic 
bones are ossified, and which appears to be continued into the membrane in front of 
Meckel’s cartilage (Plate I. fig. 3, m c), now ossified as the inferior maxilla (Plate I. 
* The specimens on which the dissections were made are in the Museum of St. Bartholomew’s Hospital. The 
figures indicating the size of each foetus give its length in inches and tenths of an inch. 
t Here and after the relations are given as for human anatomy. 
