440 Julia B. Platt 
The first functional activity of the muscle must consequently be 
exerted by pulling the skin. With the development of cartilage, 
however, the chief distal attachment is transferred to a neighboring 
branchial bar. 
Fig. 55 also shows an outgrowth from the ventral part of the 
glossopharyngeal muscle (gm) which is not found in connection 
with the mesothelium of the younger embryo. This outgrowth is 
the beginning of the muscle cerato-hyoideusinternus. In fig. 13, 
pl. XVHI, a section through the left half of the glossopharyngeal 
arch is seen, in a plane similar to that of fig. 56. The figure shows 
the beginning of the muscle cerato-hyoideus internus in the 
mesothelial tissue of the glossopharyngeal arch, which is still dis- 
tinguished by yolk granules. The section is bounded above and at 
the left by the posterior wall of the hyobranchial cleft. The heart 
and pericardium are seen in the figure below and at the right. From 
the wall of the pericardium the mesothelial tissue extends into the 
glossopharyngeal arch, and the anterior prolongation of this tissue 
towards the hyobranchial cleft is the beginning of the muscle 
cerato-hyoideus- internus. This muscle is innervated by the 
glossopharyngeal nerve, and is consequently shown by its innervation 
as well as by its origin to belong to the third arch. The muscle 
ultimately connects the cartilaginous bars of the second and third 
arches. 
In fig. 5d a pair of muscles appear which are not derived from 
the mesothelial tissue of the branchial arches, the muscles genio- 
hyoidei (gh). These muscles form part of the hypoglossus muscu- 
lature, and their origin will be described later. 
In the embryo of 15 mm, represented in figs. 6 a—6 e, pl. XVII, 
and 7a@—7e, pl. XVIII, the mandibular muscle has nearly lost its 
connection with the muscle mylo-hyoideus, and has become divided 
into two parts (figs. 65 and 74), an external part, the masseter 
muscle, which extends dorsalwards and ultimately becomes attached 
to the auditory capsule, and an internal part, the muscle temporalis, 
which also extends dorsalwards, and ultimately becomes attached to 
the dorsal wall of the skull. Both muscles are supplied by the 
trigeminal nerve. 
In the embryo of 15 mm, the hyoid muscles have also become 
distinct. The most dorsal of these muscles lies above the plane of 
fig. 6a, for the mesothelium of the hyoid arch extends dorsally to 
the ventral wall of the auditory capsule, as seen in fig. 26, pl. XVIII, 
