54 S- GOTO. 



but in the dorsal and ventral parts, they are situated directly inside 

 the external limiting membrane (PL IV, fig. 2). Some of the ex- 

 ternal circular fibres deviate more or less from their course, and passing 

 between the bundles of the lateral longitudinal fibres, are inserted 

 into the external limiting membrane. The longitudinal fibres are 

 divided into three groups, which may be called according to their 

 relative positions, thie internal, the middle, and the external. The 

 internal longitudinal fibres are present only in the posterior third of 

 the pharynx, and are situated between the inner limiting membrane 

 and the inner circular fibres (PI. IV", fig. 3, d). They do not form 

 any definite bundle, and are , inserted by their ends into the inner 

 limiting membrane of the pharynx. The middle longitudinal fibres are 

 arranged in a single layer directly on the outer side of the inner 

 circular fibres, with which they are intimately associated throughout 

 their whole course (PI. IV, figs. 2 and 3, c). The individual fibres of 

 this group are separated from one another by an intervening space, 

 and have a round outline in cross-section. The outer longitudinal 

 fibres are present only in the posterior two-thirds of the pharynx, 

 and are divided into four groups, crescent-shaped in cross-section, 

 and placed symmetrically in the lateral, dorsal, and ventral parts 

 (PI. IV, figs. 2 and 3, b and V). The lateral groups are situated 

 directly inside the external limiting membrane of the pharynx ; but 

 the dorsal and ventral groups are separated from it by the external 

 circular fibres already described. The constituent fibres of these 

 groups are formed into strong, compact bundles, which are separated 

 from one another by the radial fibres and also to some extent 

 by the external circular fibres (fig. 2). They are inserted, 

 posteriorly into the lining membrane at the end of the pharynx 

 and more anteriorly into the external limiting membrane at 

 various points. 



