158 Mr. A. Tulk on the Anatomy 0/ Phalangium Opilio. 



The posterior and inferior margins of this, the epipharynx (so 

 called, as will be seen hereafter, in treating of the digestive or- 

 gans, from its lying upon the pharynx, or rather inclosing that 

 portion of the alimentary canal), are prolonged backwards, to 

 form two elongated projections (/) directed slightly outwards, 

 nearly of equal width throughout, having the superior margin 

 concave, the inferior somewhat convex, and terminating by an 

 abrupt truncated extremity. Below, the epipharynx is hollowed 

 out (PI. III. fig. 5. w) by being bent laterally upon itself, in the 

 direction downwards, the margins of the inflections being pro- 

 longed inwards in an angular form, and serving to define or se- 

 parate the borders of the cavity into two distinct portions ; an 

 anterior, obovate, with the large end directed forwards, and the 

 plane of the opening being obliquely upwards, while the poste- 

 rior, expanded behind and narrower in front, is circumscribed 

 by the divergent angles above mentioned (/). At the point of 

 attachment of the septum the upper surface is depressed, and 

 occasionally furnished with a cluster of small spines (*), and 

 upon either side it is bounded from the lateral prolongations by 

 a transverse, thick and cartilaginous ridge (^), continuous with 

 their superior and inferior margins. Situated upon the upper 

 surface, on either side of the base of the posterior angles, are two 

 short, conical and cartilaginous projections (A), directed obliquely 

 outwards upon the sides of the basal joint of the chehcerae. 



The labrum or epistome (/), which overlies the oral aperture, 

 is a cartilaginous, papilliform and hollow structure, prolonged 

 by its base from the anterior extremity of the epipharynx. It 

 has a few bristles upon its upper convex surface, and the inferior 

 surface is concave. 



The internal surface of the cephalo-thorax presents several 

 grooves or ridges corresponding with the external elevations or 

 -depressions. A transverse posterior groove, defining its limits 

 from the abdominal cavity ; a middle triangular fossa, having in 

 its centre a nearly circular opening, leading into the deep cavity 

 of the ocular tubercle; on either side, anteriorly, the elliptical 

 opening of the lateral eyes ; and internal to these, two wide and 

 oblique grooves, bounded externally by a narrow ridge. 



Upon either side of the basal joints of the chelicerse, externally, 

 two cartilaginous pieces (PI. III. figs. 3 and 5. bp) descend ver- 

 tically from the antero-lateral angles of the thoracic shield. They 

 are of an elongated and irregularly triangular shape, their bases 

 being directed downwards, and presenting upon their anterior 

 surface an elevated articular cavity (PI. III. fig. 5. h) for the re- 

 ception of the first free joint of the palpus (2), whilst, beyond 

 this point, an expanded prolongation passing inwards towards 

 the median line constitutes the first pair of jaws (i). This cavity 



