DEVELOPMENT OF THE PHARYNX. 987 
inner wall by the aryteno-epiglottic fold, and slightly below by the upper part of 
the cricoid cartilage. 
Vessels and Nerves of the Pharynx.—The arteries of the pharynx are derived from—l, 
the ascending pharyngeal; 2, the ascending palatine branch of facial; 3, the posterior palatine, 
from the internal maxillary, with a few twigs from the dorsalis lingue, tonsillar (of facial), 
vidian, and pterygo-palatine of the internal maxillary. The veins go to the pharyngeal venous 
plexus, which is found between the constrictors and the bueco-pharyngeal aponeurosis. The 
plexus communicates with the pterygoid plexus above and with the internal jugular or facial 
vein below. 
The lymphatics of the pharynx pass chiefly to the upper set of deep.cervical glands. Those 
from the upper part of the posterior wall join a few post-pharyngeal glands which are found on 
each side between the pharynx and the rectus anticus major muscle. These latter glands, which 
are large in the child, small in the adult, but apparently always present (Fig. 664), are of con- 
siderable clinical interest, as they often form the starting-point of post-pharyngeal abscess. 
The nerves of the pharynx, both motor and sensory, are derived chiefly from the pharyngeal 
plexus, which is formed by branches of the vagus, glosso-pharyngeal, and sympathetic. The 
soft palate and the neighbourhood of the tonsil are supplied by the posterior and external 
palatine branches of Meckel’s ganglion. The tonsil receives a branch from the glosso-pharyngeal 
direct. The vault of the pharynx, and the region around the Eustachian orifice, as well as the 
orifice itself, are supplied by the pharyngeal branch of Meckel’s ganglion. Finally, the superior 
laryngeal nerve supphes the mucous membrane of the back of the larynx, where it forms the 
anterior wall of the laryngeal portion of the pharynx. 
Structure of the Pharyngeal Wall.—The pharyngeal wall is made up of 
the following layers:—(1) The thick mucous membrane, which is plentifully supplied 
with racemose mucous glands, and lymphoid tissue, and is lined by stratified squamous 
epithelium, except in the naso-pharynx, where the epithelium is columnar and ciliated. 
(2) Outside the mucous membrane lies a layer of firm connective tissue, the pharyngeal 
aponeurosis, Which is closely associated with the muscles, and receives the insertions of 
many of their fibres. This layer blends with the periosteum of the base of the skull 
superiorly, and is united to the Eustachian tube, the margins of the posterior nares, and the 
other fixed points to which the pharynx is connected anteriorly. It is thickest above, 
at the sinuses of Morgagni, where the muscular coat is wanting, and where it forms the 
chief constituent of the pharyngeal wall. Below, it gradually grows thinner as the lower 
end of the pharynx is approached. (3) External to the pharyngeal aponeurosis lies the 
muscular coat, formed of the three constrictors with the stylo- and palato-pharyngeus. 
The muscular coat is covered externally by (4) the bucco-pharyngeal fascia, a thin and, 
in places, ill-defined layer of fascia which surrounds the constrictors of the pharynx, and 
passes forward above to cover the outer surface of the buccinator. It is connected behind 
to the prevertebral fascia by loose connective tissue (the retro-pharyngeal space), and 
it is similarly connected by areolar tissue to the other structures with which the pharynx 
comes in contact. 
The racemose glands of the mucous membrane, which are of the mucous type, are 
very numerous in the walls of the naso-pharynx and in the soft palate, where they form 
a thick continuous layer. They are also numerous about the aryteno-epiglottic folds and 
on the back of the arytenoid muscles in the laryngeal portion of the pharynx. Over the 
rest of this cavity, though numerous, they are not so thickly placed as in the regions just 
mentioned. The lymphoid tissue, either in a diffuse form or collected into lymphoid 
follicles, is found throughout the whole of the mucous membrane. As already pointed 
out, it is particularly abundant on the upper portion of the posterior wall of the naso- 
pharynx, where it forms the pharyngeal tonsil. 
The pharyngeal aponeurosis, which is thick above and thin below, and the bucco- 
pharyngeal fascia, which is thin above and stouter below, are practically blended into one 
layer above, near the base of the skull, where the muscular coat is absent. Lower 
down they are separated by the constrictors, and become two distinct sheets. They 
are strengthened in the middle line posteriorly by a fibrous band descending from the 
pharyngeal tubercle. 
DEVELOPMENT OF THE PHARYNX AND TONSIL. 
For the development of the pharynx from the anterior portion of the foregut, and the 
formation and fate of the visceral arches and clefts which are found in its wall, the reader 
is referred to the chapter on General Embryology, p. 32. 
The anterior palatine arch is derived from the second visceral arch, behind which, in 
the embryo, lies the pharyngeal portion of the second visceral cleft. This cleft is crossed 
