SOME OF THE SHE A XT A L ARCHES IN MAN. 
121 
fig. 3, m ) or mandible : Meckel’s cartilage is seen growing out beneath the membrane 
and then passing under cover of the lower jaw. 
In a foetus 1*8 long, tenth to eleventh week, the lingual arch consists of five portions, — 
(1) cartilage from the base of the skull, (2) a short piece of membrane, (3) a second 
very small and short rod of cartilage, these three structures having a length of -09 of an 
inch (Plate I. fig 5, l to l *), (4) a long strip of membrane, and (5) a nodule of cartilage 
at the anterior extremity of the arch, which is connected with the hyoid below. The 
entire length of these structures is T9 of an inch. 
The Fifth Suhaxial Arch — The Hyoid. 
On a deeper plane and under cover of the parts in which the lingual arch is formed, 
a layer of membrane, comparatively broad, is seen growing out from the base of the 
skull in connexion with that part in which the basioccipital ossification takes place. In 
a foetus T5 long it has the form shown in Plate I. fig. 1. This mass widens as it 
descends into the cervical region and towards the middle line, and divides into two chief 
parts ; the higher of these is the hyoid arch. 
This arch is at first represented by the upper portion of the layer of membrane, and 
by a bud of this membrane from the upper and mesial extremity of either side piece 
(Plate I. fig. 1, h). These buds meet in the middle line and there unite, so that in a 
foetus '9 long they form a distinct rod, now cartilaginous as far back as the point h *, 
fig. 2, rather less than T of an inch long, where it is connected with the mass of mem- 
brane continued down to the larynx. The band of tissue connecting this arch with the 
thyroid cartilage at the point h *, fig. 2, is now just discernible; in the next dissection? 
that of a foetus 1'2, it is distinctly formed. The higher portion of this arch, towards 
the base of the skull, forms the middle constrictor muscle, which in a foetus T8 can be 
traced from the base into the posterior portion of the cartilage of the arch, the greater 
or posterior horn of the hyoid bone. 
The posterior portion of this arch, therefore, is membranous, and developes into the 
middle constrictor muscle ; the cartilage in the anterior two-thirds ( - 06 long in a foetus 
of "9, and IT in a foetus of T8) consists of two portions, the one the greater horn, the 
other the body of the hyoid bone. 
The Sixth Suhaxial Arch — The Laryngeal. 
Whilst the upper portion of the layer of membrane from the basioccipital cartilage 
grows forward to form the hyoid arch, the lower division, first distinctly separated from 
the upper by anterior bud-like outgrowths, forms a mass in the cervical region which in 
a foetus of '45 is about '05 of an inch in length (Plate I. fig. 1, Ig). This mass, uniting 
with a corresponding growth from the opposite side, forms an irregular line in the middle 
of the neck, all trace of which line rapidly disappears. At first it lies flat upon the ver- 
tebrae, but quickly thickens, and in a foetus '9 forms a thick block advanced to the level 
of the anterior extremity of the lingual arch (Plate I. fig. 2, th, cr). As it thickens 
