MOUTH PARTS : BUCCAL CAVITY 65,9 



mid-intestine with a pair of scissors ; all tracheal twigs, the Malpighian 

 tubes, connective tissue and other structures should be removed. If 

 necessary the parts should be flushed with saline and 



fresh solution added to the trough. On lifting up the Tl \ e fop e-. inte8tine : - 



, b dissection to ex- 



anterior end of the mid-intestine the delicate oesop- pose the parts 



hagus is seen entering it on its posterior surface. 

 When this is followed forwards it is found to pass downwards and to 

 enter a large white structure, the brain, from the anterior end of which 

 it emerges to unite with the pharynx. The brain should be carefully 

 lifted up and the nerves passing from it divided ; the adjacent parts 

 should be cleared of all tracheae, care being taken not to damage the 

 salivary ducts. When this preliminary dissection has been completed it 

 will be seen that a triangular area has been exposed (Plate LXXXIII, 

 fig 3). The apex of this triangle is situated at the base of the capitulum 

 and of the chitinous mouth parts ; laterally it is enclosed by the salivary 

 glands and their ducts, and posteriorly by the oviducts and mid- 

 intestine. The brain lies deep down about the centre of the area, and is 

 traversed from before backwards by the oesophagus as it passes to enter 

 the mid-intestine ; the pharynx lies at the apex of the triangle and 

 may be recognized by its fusiform shape. Although the formation of 

 the buccal cavity and the adjacent parts is most satisfactorily studied in 

 transverse and longitudinal sections of the capitulum, the general 

 arrangement and relations of the various structures can be made out in 

 an ordinary dissection. 



For descriptive purposes the buccal cavity may be divided into two 

 parts, only one of which, the posterior, is completely closed. The 



anterior part is a flat tube, the dorsal wall of which is . 



The buccal cavity. 

 formed by the apposition of the two mandibles and plate LX xxv 



their sheaths, the ventral by the hypostome. In the 

 normal resting condition this tube is open at the sides (Plate LXXXV, 

 fig. 2), and the two walls can be separated by a needle. When the tick 

 is attached to its host, however, the mouth parts are embedded in 

 the skin, which closes the sides of the buccal cavity. The posterior part 

 is closed at all times. The mandibular sheaths fuse with each other in 

 the middle line, and with the hypostome at the sides, about the level of 

 the lower third of the second palpal segment, though the exact position 

 varies in the different species ; the dorsal integument of the basis 

 capituli passes forwards to fuse with the basal joints of the palps and the 

 sheath of the mandibles, and the ventral integument blends with the 

 .hypostome. The chitinous ring which is thus formed is spoken of 



