442 Prof. Mautosh on the 



to tlie arcli o£ tlie canal. It is now noticed that the wall of 

 the pharynx is greatly thickened by muscular layers, which — 

 Avith the massive retractors — fill up a large part of the body- 

 cavity superiorly. The insertions of the great retractors in 

 the lateral regions are crossed by the circular fibres^ which 

 extend from the superior fold (beneath the arch) of one side 

 to that of the opposite, thus forming a strong constricting 

 layer, very well marked inferiorly. External to the latter at 

 the ventral surface is a complex layer consisting of longi- 

 tudinal fibres mixed with a radiating series which pass from 

 the inner margin through the circular coat. Behind the 

 foregoing the attachment of the retractors to the superior 

 raphe is evident, the breadth of the circular layer is increased, 

 especially inferiorly, and the vertical series, which radiate 

 downward through the latter, form a prominent mass — 

 striated with cross-fibres — inferiorly. The ventral region 

 or floor of the pharynx has again opened out into a less 

 compact and apparently a chitinous tissue. The structure 

 remains similar in the next section superiorly, but inferiorly 

 the mobile glandular region of the pharynx appears in the 

 middle of the great muscular mass, the sides and ventral 

 region being formed by a complex meshwork of muscular 

 fibres — longitudinal, oblique, and radiating — which connect 

 the inferior to the superior mass. In full development this 

 system shows a great central region of folded glandular 

 tissue, surrounded superiorly by the circular fibres and the 

 retractors, laterally and inferiorly by the densely interlaced 

 muscular fibres, those next the canal^ however, being chiefly 

 circular in direction. The muscular envelope next diminishes 

 in thickness, and is confined for the most part to the lower 

 half of the canal. Within is the circular coat, which pro- 

 ceeds almost to the superior arch (in transverse section) ; 

 then inferiorly is a considerable belt of longitudinal fibres 

 with interfascicular substance. This coating descends lower 

 until it forms — for the somewhat specialized ventral floor 

 of the region — an inner strong circular band, and a radiated 

 mass (with longitudinal fibres) nearly as broad beneath, the 

 fibres passing vertically through the former to the glandular 

 border. This complex arrangement — diminishing to a mere 

 speck — finally disappears, and leaves the chamber surrounded 

 only by its proper walls, which at the termination of the 

 pharyngeal portion are a thick basement-tissue and an outer 

 layer of longitudinal and circular fibres. 



The pharyngeal region is interesting as containing that 

 portion of the canal which, to a greater or less extent, is 

 thrust into the proboscis in extreme extrusion, and the 



i 



i 

 1 



