THE PHARYNX. 1603 



2 cm. in front of the vessel. The external carotid is placed more directly outward and 

 is rather the nearer of the two. The parotid gland, according to Tillaux, sends a 

 process in front of the styloid process, which reaches the lateral wall. This extension, 

 however, does not seem to be by any means constant. 



Development and Growth of the Pharynx. — An account of the formation 

 of the primitive pharynx is included in the Development of the Alimentary Tract 

 (page 1694), the later changes being here noted. In the section on the bones it was 

 shown that the chief peculiarities of the infant skeleton in this region are due to the 

 small size of the face and the more horizontal base of the skull. The naso-pharynx 

 has very little height, while, owing to the peculiar disposition of the parts, it has nearly 

 the same antero-posterior diameter as in the adult. It is relatively broad and long, 

 but very shallow. The tongue, in proportion, is much less thick at the base than 

 later. The larynx is small, and, moreover, is placed higher in relation to the vertebral 

 column, so that the termination of the pharynx is also higher. The position of the 

 larynx at different ages is considered with that organ (page 1828). The soft palate is 

 in the main horizontal at birth and about on a level with the top of the atlas. The 

 uvula is rudimentary. In a child of probably not over three years we have found 

 the tip of the uvula rather below the middle of the body of the axis. In Symington's 

 section of a girl of thirteen it is pretty nearly in the adult position. In infancy the 

 soft palate probably closes the passage into the naso-pharynx from below less perfectly 

 than later. 



The opening of the Eiistachiaji tube, although necessarily in the naso-pharynx, 

 is in the foetus below the level of the hard palate. At birth it is at about that level, 

 but rather below than above it. According to Disse, there is but little change for 

 nine months, after which the opening is on the level of the inferior meatus. Proba- 

 bly the adult position is generally reached after puberty. The opening is small 

 in the infant and young child, and, owing to want of development of the cartilage, 

 there is but a slight elevation about it and consequently but a small fossa of Rosen- 

 miiller. The entire adenoid system of this region ^ has made but little progress 

 before birth. 



At birth the pharyngeal tonsil is a very small collection of adenoid tissue at the 

 back of the roof, covered by more or less converging folds of the mucous membrane. 

 It is not necessarily present. During the first year it grows rapidly, and particularly 

 forward, so that by the end of that time it extends to the back of the upper margin of 

 the choanae. Under normal conditions the pharyngeal tonsil retains its relative size 

 to the cavity of the pharynx up to twelve years ; but during this time the total amount 

 of adenoid tissue has decidedly increased, owing to the development of the tubal 

 tonsils. 



The faucial tonsils are developed in a recess of the primitive pharynx between 

 the second and third visceral arches. By the fourth foetal month the tonsillar anlage 

 presents a number of slit-like depressions, lined with entoblastic epithelium, from 

 which secondary epithelial sprouts invade the neighboring mesoblast. This process 

 continues after birth during the first year. The young connective tissue surrounding 

 the epithelial sprouts — the latter being at first solid, but later possessing a lumen — 

 becomes infiltrated by accumulating leucocytes and gradually assumes the character 

 of adenoid tissue, the differentiation into distinct lymph-nodes, however, being delayed 

 until after birth. The source of the lymphoid cells is a matter of dispute. Accord- 

 ing to some, these elements are leucocytes from the. circulation caught within the 

 young connective tissue ; others maintain that they are derived from the transforma- 

 tion of the epithelium, the lymphoid tissue resulting from the mutual invasion and in- 

 tergrowth between the ento- and mesoblastic elements. According to Hammar,' who 

 has carefully studied the development of the tonsils, the lymphoid cells are derived 

 chiefly from the fixed connective-tissue elements. At birth the tonsils are insignifi- 

 cant, but grow rapidly during the first year. At from the twelfth year to puberty 

 the entire adenoid system of the pharynx enters upon a stage of retrogression. In 

 the adult the pharyngeal and tubal tonsils are much smaller ; after middle age they 

 undergo atrophy. 



^ Escat : Evolution de la Cavit6 Naso-Pharyngienne, 1894. 

 ^ Archiv f. mikro. Anat., Bd. xli., 1902. 



